Identify two main ideas about the normal force.

Due to Newton's third law, the normal forces will be equal in magnitude and in opposite direction. The normal force always makes a 90 degree angle with the surface (perpendicular).

Explanation:

1/0.14nm = 10^10/1.4 a lot

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.