Greg had homework in math, science, and English. He spent 45 minutes on his science homework and 30 minutes on English. If he spent 2 hours on his homework in all, which number sentence should you use to find out how long he spent on math?
A. 120 - (45 + 30) =
B. (45 + 30) ÷ 2 =
C. (45 + 30) - x = 120
D. 2 + (45 - 30) =
E. Other