Beneath Earth’s surface, the temperature increases 10°C for every kilometer closer to the center. Suppose that the surface temperature is 22°C, and the temperature at the bottom of a coal mine is 45°C. Which equation could be used to find the depth d of a coal mine?

a. 10d + 22 = 45

b. 45d – 10 = 22

c. d = 22 + 10

d. 22 = 10d + 45