The easiest way to make .15 a fraction would be to put 100 under it, making it 15/100.
But now it needs to be simplified. Find a number that goes into both the numerator and the denominator easily. In this case we can say 5.
Divide both numbers by 5:
15/5 = 3
100/5 = 20
Now our numerator is 3, while our denominator is 20, making your answer 3/20