Question

Polly is pushing a box across the floor with the force 30 n the force of gravity is -8n and the normal force is 8n which value could describe the force of friction if Polly could not move the box

Answer 1

The normal force is 8N.
The force applied (assumed horizontal) is 30 N
Coefficient of friction >= 30/8=3.75 (unusual).

In any case, the FORCE of friction is equal and opposite to the applied horizontal force, if the box remained stationary.