## Precalculus (10th Edition)

$56$
If we approximate the area using the left endpoints, then: $A=(2-0)f(0)+(4-2)f(2)+(6-4)f(4)+(8-6)f(6)\\=2f(0)+2f(2)+2f(4)+2f(6)\\=2(10)+2(5)+2(7)+2(5)=56$