Plug the numbers into the formula, V=πr2h, you know that your radius is 3 and your height is 5, so you get V=π(3)2(5), you just then put it in the calculator. You get 141.37, round to the nearest tenth 141.4
Your calculator says error because you cant have a square root of a negative number because there is no solution to that maybe recheck your equation and try again
