A plumber earns $40 an hour and the plumber's helper earns $25 an hour. One day the helper starts work at 8 a. m. and the plumber starts at 10 a. m. They both continue working until 4 p. m. The following equations can be used to determine each person's earning, where a represents the amount earned and x represents the number of hours that have passed since 8 a. m. PLUMBER: a = 40(x - 2)
HELPER: a = 25 x

At what time will the helper and the plumber have earned the same amount of money?
A: 1:13 p. m.
B: 1:20 p. m.
C: 3:13 p. m.
D: 3:20 p. m.