To keep in shape, Dominic exercises at a track near his home. He requires 15 minutes to do 5 laps running and 2 laps walking. In contrast, he requires 36 minutes to do 6 laps running and 6 laps walking. Assuming he maintains a consistent pace while running and while walking, how long does Dominic take to complete a lap?
a. 3 minutes
b. 4 minutes
c. 5 minutes
d. 6 minutes