There seems to be inconsistency in this question.
∫(3.5-4f(x))dx=3, so 3.5x-4∫f(x)dx=3, 4∫f(x)dx=3.5x-3.
∫(-1.5-4f(x))dx=8, so -1.5x-4∫f(x)dx=8, 4∫f(x)dx=-1.5x-8.
Therefore, 3.5x-3=-1.5x-8, 5x=-5, x=-1. And 4∫f(x)dx=-3.5-3=1.5-8=-6.5.
∫f(x)=-6.5/4=-1.625.
∫(1-1.5f(x))dx=x-1.5∫f(x)dx=-1+1.5×1.625=-1+2.4375=1.4375.
The remaining parts of the question seem to be superfluous and inconsistent.