Work backwards
First, Subtract 9 dollars (That he just earned form washing car) from the 15 he ended up with,so that you get what his leftover money from the movie was.
15-9=6, 6 * 2 = 12
So benny started with 12 dollars as a weekly allowance
Double check by going in order
12/2 = 6 (He spent half original amount on movies), then add 9 for his chore
6+9=15, 15 is what his end amount was so the answer is $12 was benny's start or weekly allowance
