A bicyclist rides with a constant velocity of 8 m/s. What would you need to know to calculate the net force on the rider?

You already have everything you need to know.  As soon as you heard "constant velocity", you knew that his speed is constant and he's moving in a straight line.  At that moment, the Physics section of your brain called out "zero acceleration !", and you knew that the net force on him must be zero.

zero                     acceleration would be your answer