I am a freshman college student and I am new to discrete mathematics. I tried to look for something in my textbook to help me figure out a problem I have but I don't really understand how to solve it. Here is the problem:

Prove by contradiction that for all x, y ∈ R, if x is rational and y is irrational, then x+y is irrational.

I'm not really sure what to do. Could I please get some help? Thank you!