Question

suppose you earn $6 per hour at your part time job. What will your new hourly rate be after a 2.5% raise.

Answer 1

The answer to your question is:

15

Because:

You multiply 2.5 and 6 to each other and get the product of:

15

Answer 2

Let if you earn $100 per hour a raise of 2.5% means you will get $102.5.
i.e 102.5% of earlier.
in case of $6, it will be its 102.5%, = 102.5*6/100 = $6.15 per hour.