For cell M50, If B50>20 then M50 = 100 but if M49>1 then M49 * 1.5
If I then copy M50 to M51,M52, M53, M54 etc, once M50 has a number the following cells will multiply that previous cell value by 1.5.
If B50 is never >20,then all M values = 0
Once B50, or B51, B52, B53 etc >20, then...