Chapter 13 - A Preview of Calculus: The Limit, Derivative, and Integral of a Function - Section 13.5 The Area Problem; The Integral - 13.5 Assess Your Understanding - Page 923: 7

$$56$$

Our aim is to calculate the approximation of $A$, the area under the function using the left endpoints. Therefore we have: $$A=(2-0)f(0)+(4-2)f(2)+(6-4)f(4)+(8-6)f(6)\\=2f(0)+2f(2)+2f(4)+2f(6)\\=2[10+6+7+5] \\ =(2)(28) \\=56$$