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

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.