First you would have to set up a proportion in which you have the 12.5% as a fraction
12.5/100
You then would multiply
$34 × 12.5 = 425
After you multiply that you then will divide
425 ÷ 100 = 4.25
Once you have that you can add the 4.25 to the $34 and see that you get exactly $38.25.