To subtract fractions, you need to have a common denominator. In this case, the common denominator is 15.

First, convert 3/5 to have a denominator of 15:
(3/5) * (3/3) = 9/15

Now, subtract the fractions:
9/15 - 4/15 = (9 - 4)/15 = 5/15

Simplifying the fraction, we get:
5/15 = 1/3

Therefore, 3/5 - 4/15 = 1/3.