What’s is the area of shape B?

I’m stuck on this i don’t understand.

Given the equation f(x)=a(b)x where the initial value is 40 and the growth rate is 20% what is f(4)

Circle a has a diameter of 7 inches, a circumference of 21.98 inches, and an area of 38.465 square inches. the diameter of circle b is 6 inches, the circumference is 18.84 inches, and the area is 28.26 square inches. part a: using the formula for circumference, solve for the value of pi for each circle. (4 points) part b: use the formula for area and solve for the value of pi for each circle. (4 points)