1. The problem statement, all variables and given/known data For region 8<x<12 , why there's an extra (60-30y +3.75y^2 ) - (30y-7.5y^2) ??? How to get that? I have no idea at all... 2. Relevant equations 3. The attempt at a solution here's my working, i have divided the triangle into three parts, i gt 129-80 -75- (60-30y=3.75y^2) - (30y-7.5y^2)-(3.75y^2) instead of 129-80 -75- (60-30y=3.75y^2) - (30y-7.5y^2) Is the author wrong?