Question

Add 10N acting left to right, to 10N acting left to right

Answer 1

When we add forces we work with vectors that have magnitude and
direction.
While adding vectors we add them by components (e.g., x-components
and y-components separately).
In this particular case both forces have the
same direction, so the resulting force will be
10H + 10H = 20H
acting left
to right.