Which one is the missing number?

Find the area of a square with a side length of 1/4 in.

Estimate the area under the curve f(x) = 16 - x^2 from x = 0 to x = 3 by using three inscribed (under the curve) rectangles. answer to the nearest integer.

How many solutions does the nonlinear system of equations graphed below have? a. one b. zero c. four d. two