Answer:
AFter 3.5 s, the wagon is moving at: 
Explanation:
Let's start by finding first the net force on the wagon, and from there the wagon's acceleration (using Newton's 2nd Law):
Net force = 250 N + 178 N = 428 N
Therefore, the acceleration from Newton's 2nd Law is:

So now we apply this acceleration to the kinematic expression for velocity in an object moving under constant acceleration:

Answer:
This is very hard bit I think 6.3 my, I'm not shure.
Total distance = 76+54 = 130km
total time = 2+5 = 7hrs
Av. speed = 130/7 = 18.571km/hr = 18.6 km/h ( 3 sig fig)