Answer:
The normal force between the motorcycle and track at the top of the loop = 2343.75 N
Step-by-step explanation:
At the top of the loop the track is directed tangential to the motion, the normal to the tangent is along radius of circle. that is here we need to find centripetal force.
We have expression for centripetal force

Here mass, m = 175 kg
Velocity, v = 7.5 m/s
Diameter, d = 8.4 m
Radius, r = 0.5d = 0.5 x 8.4 = 4.2 m
Substituting

The normal force between the motorcycle and track at the top of the loop = 2343.75 N