Reconstruct a question, answer pair from this explanation: The clown is holding 3 x 12 = 36 balloons. This many children buy a balloon: 3 + 12 = 15 kids. After the children buy the balloons, the clown is holding this many in his hand 36 - 15 = 21 balloons.
Q:At the circus, the clown has 3 dozen balloons on a string in his hand. 3 boys and 12 girls buy a balloon each. How many balloons is the clown still holding?
A:21