Hey there!
When calculating for percentages of numbers, you first have to convert your percentage into a decimal. You can do this by dividing it by 100. In this case, you can divide 8 by 100 to get 0.08. You can then use this to solve by multiplying it by your other given number, $1500.
1500 × 0.08 = 120
Since the problem wants you to only list how much more Tim will pay, you don't need the total. This means your answer is $120. Pay close attention to that part of these questions in the future!
Hope this helped you out! :-)