Describe some advantages and disadvantages of observing the Sun (a) from space and (b) from Earth's South Pole. What kinds of phenomena and issues do solar astronomers want to explore from both Earth-orbiting and Antarctic observatories?

Solar astronomy is the scientific study of the celestial star we refer to as the sun and the phenomena that surround it. The main concerns of solar astronomy are the physics, chemistry, meteorology, motion and evolution of the sun as well as its place in the universe.

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.