A point (x, y) is randomly chosen such that 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. What is the probability that y ≤ 2x - 1?

Look at the answer to the question here: https://web2.0calc.com/questions/real-numbers-x-y-are-randomly-chosen-from-the-interval#r1

With a small modification you should be able to use this to answer your question.