Brian's final exam in math had two parts. He had a total of 60 minutes to complete the entire exam. He spent 15 minutes on Part 1 of the exam. Write and solve an equation to show how much time he had left to complete Part 2.

m over 15 equals 60; m = 900 minutes
m − 15 = 60; m = 75 minutes
15 + m = 60; m = 45 minutes
15m = 60; m = 4 minutes