Accounting for labour

Hi Mr John, I tried doing this qn on the course note but the ans I got was inncorrect. As such, I would like to know where did I go wrong.

An employee is paid on a piecework basis as follows:
1 to 500units – $0.50 per unit
501 to 1000 units – $0.75 per unit
1001 to 1500 units – $1.00 per unit
Only the additional units qualify for the higher rates and rejected units do not qualify for payment. During one day, an employee produced 1200units of which 32 were rejected.
How much did the employee earn for the day?
a) $825
b) $1200
c) $793
d) $1168

My working for this qn was:
Good quality: 1200units – 32units = 1168units
1st 500units: 500x$0.50=$250
leftover units (668units): 668x$0.75=$501
Total amt earned: $250+$501=$751

The ans I got is not one of the option. Pls help! thanks!