Help. Don't know what formula to use. Can you figure this out?

[st600r]

<colgroup><col style="mso-width-source:userset;mso-width-alt:7008;width:164pt" width="219"> <col style="width:82pt" span="7" width="109"> </colgroup><tbody>
[TD="class: xl71, width: 219"] 1998 Porsche Boxster
[/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]
[TD="class: xl65, width: 109"] [/TD]

[TD="class: xl67"]Today's Date[/TD]
[TD="class: xl68"]15-Sep-2013[/TD]
[TD="class: xl68"]2-Apr-2015[/TD]
[TD="class: xl68"]9-Jul-2015[/TD]
[TD="class: xl68"]4-Aug-2015[/TD]
[TD="class: xl68"]13-Sep-2015[/TD]
[TD="class: xl68"]16-Sep-2015[/TD]
[TD="class: xl68"][/TD]

[TD="class: xl70"] Mileage [/TD]
[TD="class: xl64"] 78,722 [/TD]
[TD="class: xl64"] 83,419 [/TD]
[TD="class: xl64"] 86,647 [/TD]
[TD="class: xl64"] 87,561 [/TD]
[TD="class: xl64"] 89,022 [/TD]
[TD="class: xl64"] 89,196 [/TD]
[TD="class: xl64"][/TD]

[TD="class: xl70"] Oil Change [/TD]
[TD="class: xl64"] yes [/TD]
[TD="class: xl64"] yes [/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"] yes [/TD]
[TD="class: xl64"][/TD]

[TD="class: xl70"] Oil Level [/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"] full [/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"] full [/TD]
[TD="class: xl64"][/TD]

[TD="class: xl72"]*****************[/TD]
[TD="class: xl73"]78,722 [/TD]
[TD="class: xl73"]83,419 [/TD]
[TD="class: xl73"] [/TD]
[TD="class: xl73"] [/TD]
[TD="class: xl73"] [/TD]
[TD="class: xl73"]89,196 [/TD]
[TD="class: xl73"] [/TD]

[TD="class: xl75"]Driven since last Oil Change[/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]
[TD="class: xl76"] [/TD]

[TD="class: xl70"] Driven since last date [/TD]
[TD="class: xl64"][/TD]
[TD="class: xl64"] 4,697 [/TD]
[TD="class: xl64"] 3,228 [/TD]
[TD="class: xl64"] 914 [/TD]
[TD="class: xl64"] 1,461 [/TD]
[TD="class: xl64"] 174 [/TD]
[TD="class: xl64"] (89,196)[/TD]

</tbody>

I AM TRYING TO FIGURE OUT HOW TO SHOW "Driven since last Oil Change".
C8:Z8 has this formula: =+C3-B3.......this gives me "mileage" driven since last date. I need to figure out what formula to use on row 7 so that I get a cumulative number showing the total mileage driven since the last oil change.
Row 6 has this formula C6:Z6. =+If(C4="yes",C3,"")
Thanks! Steve

 

[Comfy]

Something like this??

Excel 2010
	A	B	C	D	E	F	G	H
1	1998 Porsche Boxster
2	Today's Date	15-Sep-13	02-Apr-15	09-Jul-15	04-Aug-15	13-Sep-15	16-Sep-15
3	Mileage	78,722	83,419	86,647	87,561	89,022	89,196
4	Oil Change	yes	yes				yes
5	Oil Level		full				full
6	*****************	78,722	83,419				89,196
7	Driven since last Oil Change		4,697	3,228	4,142	5,603	5,777
8	Driven since last date		4,697	3,228	914	1,461	174	-89,196
Sheet1

Cell Formulas
Range	Formula
C7	{=C3-INDEX($B$3:B3,,MAX(($B$4:B4="yes")*(COLUMN($B$4:B4)-COLUMN($B$4)+1)))}
Press CTRL+SHIFT+ENTER to enter array formulas.

 

[st600r]

Comfy, thank you. That is incredible.

 

[FDibbins]

Cross-posted here...
Help. Don't know what formula to use. Can you figure this out?