a is going to be the first speed. But it's 2 km/h, and t is supposed to be in minutes, so convert: .
The second speed is going to be .
Note that the speed changes after 45 minutes. We need to know the distance traveled: .
The equation find the distance after having run for 45 minutes @ 2 km/h would be
so b = 1/15 and d = -1.5.