Answer:
310.5 J
Explanation:
The total work done by Martha is equal to the increase in gravitational potential energy of the package, which is equal to

where
(mg) = 45 N is the weight of the package
is the increase in height of the package
The package is carried up 3 flights of stairs, each one with a height of 2.3 m, so the total increase in heigth is

And so, the work done by Martha is

Protons and neutrons in an atom are held together by a nuclear energy also called the strong force.
True
False
True
My answers
That's called the "normal" to the surface at that point.