Answer:
To find the magnitude force with which the floor pushes up on the scale, we need to subtract the weight of the scale from the weight of Margie.
Margie weighs 428 N and the scale weighs 55.0 N. Therefore, the net force acting on the scale is:
Net force = Margie's weight - Scale's weight
Net force = 428 N - 55.0 N
Net force = 373 N
So, the magnitude force with which the floor pushes up on the scale is 373 N.