Answer:
5 bricks.
Explanation:
Comment
This is the kind of question where you have to invent your own formula. It is not obvious what to do.
Formula
Ff (frictional force) = mu (coeficient of friction) * weight of 1 brick * Number needed.
FF(friction force) = mu * weight 1 brick * number of bricks.
Givens
ff = 80 N
mu = 0.8
Brick weight (1 brick) = 20N
n is the number of bricks needed.
Solution
Ff = mu * weight 1 brick * number of bricks Substitute the givens
80 = 0.8 * 20N * n n is the number of bricks
80 = 16 * n Divide by 16
80/16 = 16*n/16
5 = n
You have to add 5 bricks.