Her weekly allowance is $20
Explanation:
Let her weekly allowance be 'a'
Given that,
She spent half of the allowance (a/2)
So,
Money left with her = (a/2)
She earned $6 by washing the car
She has $16 at the end.
So,
(a/2) + 6 = 16
(a/2) = 16 - 6
(a/2) = 10
a = 10 x 2
a = 20
So, her weekly allowance is $20