(sum of((1+3*((120+a)/(60/0.9)-1.5)) * 0.9*1/60) a=0 to x ) = 1- (1+3*((120)/(60/0.9)-1.5)) * 0.9*10/60 - (1+3*((124)/(60/0.9)-1.5)) * 0.9*4/60 - 4* (1+3*((124)/(60/0.9)-1.5)) * 0.9*(1/4)/60