Question

Danielle spent half of her weekly allowance at the movies. To earn more money her parents let her wash the car for $7. What is her weekly allowance is she ended with $16

Answer 1

Just subtract

16 - 7 = 9

9 * 2 (since she spend HALF of her allowance)
9*2 = 18

Answer: Her weekly allowance is $18

Answer 2

If at the end of all of this she ended up with 16 dollars, then we can work the problem out in this fashion:
She made 7 extra dollars on top of the half of her weekly allowance that she had remaining. Therefore, we need to subtract 7 from 16 to see what that half was. 16 - 7 = 9
9 is half of her weekly allowance, and by doubling it, we get 18.
Danielle's weekly allowance is $18.
Hope this helped! =)