You use the equation 3.14r^2, for your problem, 3.14(5^2). Then you get 3.14(25) and guessing without using a calculator, you can see that it's going to be at least three times itself but not yet four. Therefore you can approximate the answer to be between 75 and 100 squared. I did this without a calculator but to get the exact answer you'd use a calculator and it would be letter B) 78.5 cm^2. Hope this helped!
