The formula for volume of a sphere is V = 4
/3 x π x r3 (cubed).
The original radius of the balloon is 10 ft, so when we plug that value into the equation we get 4188.79. When the balloon deflated, the new radius was 5 ft, so the new volume is 523.6. The question asks how much volume was lost, so we need to subtract 4188.79 - 523.6 and get approximately 3665.
Hope this helps! I hate taking usa test prep quizzes too haha.
