Answer:If Mary spent half of her allowance the equation will begin with 1/2x or 0.5x where x is her allowance and 0.5 is half of her allowance spent. Mary also earned 7 dollars by washing the car so this will be added to her allowance spent.
The problem says that after Mary has spent half of her allowance at the movies she was left with 18 dollars so that means that the equation must be equal to 18.
The answer is 20 because you have to subtract 7 from 17 because you work backwards. Then you are left with 10, which is half of 20. So, her weekly allowance is $20
