Abicyclist 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.

The car would move to the right with 150 n of force. the 150 n of force from friction and air resistance slows the car from moving to the right with 300 n of force.