ok so 68 customers everything morning times 7 days per week is 476 customer.
now we know that 476 x .67 = $318.92
she make 8.50 per week plus $318.92 from customers
now we have this equation of
500 = 8.5x + 318.92
find x you will know how many weeks she needs.
8.5x = 500 - 318.92
8.5x = 181.08
x = 181.08/ 8.5
x ~~ 21.3 weeks