Answer
$A=239~in^{2}$
Work Step by Step
The area of the side of the tire is the area of the outer circle minus the area of the inner circle.
We use the area of a circle:
$A=\frac{\pi*d^{2}}{4}$
With the two different diameters and subtract the difference. Thus, we have:
$A=\frac{\pi*dout^{2}}{4}-\frac{\pi*din^{2}}{4}=\frac{\pi*(23in)^{2}}{4}-\frac{\pi*(15in)^{2}}{4}=238.76in^{2}\approx239~in^2$
