This problem has to do with the normal acceleration increasing/decreasing in the dips and bumps of the road. I would need the weight of the cars to get an exact answer so I will answer these in terms of the mass m.
a) In this one we don’t need to worry about the normal acceleration since there is no curve.
at = uk*Fn
Fn = mg = 9.81m
at = 1*9.81m = -9.81*m
this is considered negative since the forward motion of the car is in the positive direction.
b) Now we will find the normal acceleration caused by the curve.
an = v^2/r = 27^2/200 = 0.135 m/s^2
Fn = m*(an+ag) = (9.81+0.135)m = 9.945m
at = uk*Fn = 1*9.945m = -9.945m
c) Since the velocity and the radius are the same the normal acceleration is the same, however this time it is in the opposite direction of gravity.
an = 0.135
Fn = (9.81 – 0.135)m = 9.675m
at = uk*Fn = -9.675m