Answer: It's a rational number.
Explanation:
Let's look at all the sets of numbers:
Whole numbers - all positive numbers + zero
Integers - all whole numbers + all negative numbers
Rationals - all integers + fractions & decimals
Irrational numbers - all numbers that cannot be written as fractions
Real numbers - all of the above.
-3/5 is a fraction, so it belongs in the rationals set and also in the real set.