[问答题]
A girl is whirling a ba 0nhbrj7r u(w o7+jpj,h54qzwt)mvq x-azc r);78d;lzwfc f4ll on a string around her head in a horizontal plane. She wants to let gotfd-vc; mzf8q xl4a))r wcz7; at precisely the right time so that the ball will hit a target on the other side of the yard. When should she let go of the string?
