Overhead cost is the Total Cost minus the cost of all inputs, in this case labor and price of parts. The Overhead Rate is this number divided by total labor hours.
Total Cost: $82.00
Labor Cost: 7.5 x 6.5 = $48.75 -
Price of parts: $0
Overhead Costs: = $33.25
Divided by labor hours ÷ 6.5
Overhead Rate = $5.12
Overhead rate is $5.12