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

[st600r]

1998 Porsche Boxster
Today's Date	15-Sep-2013	2-Apr-2015	9-Jul-2015	4-Aug-2015	13-Sep-2015	16-Sep-2015
Mileage	78,722	83,419	86,647	87,561	89,022	89,196
Oil Change	yes	yes				yes
Oil Level		full				full
*****************	78,722	83,419				89,196
Driven since last Oil Change
Driven since last date		4,697	3,228	914	1,461	174	(89,196)

<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>
</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?