A person pushed on the petal of a bike and causes it to move to the left. The applied force was 85 N left and the force of friction was 12 N right. Find the net force

The net force is 73 N to the left

Explanation:

The net force f = applied force, F + frictional force, f'

f = F - f'

If we take right as positive,

F = -85 N (since it is to the left) and f' = +12 N (since it is to the right)

So, f = F + f'

f = -85 N + 12 N

f = -73 N

So, the net force is 73 N to the left

i don't understand. explain it clearly