What is the value of g at a distance of five times the Earth's radius when earth's surface is 9.8m/s^2?

Answer 1

The formula you need is:
g = G*m1*m2/r^2
where m1 and m2 are the masses of the 2 objects. In this case, m2 (you) is negligible compared to m1, so it's ignored.

g = G*m1/r^2

If only r^2 is changing, then g changes by 1/r^2.
9.8 * 1/25 = 0.392 m/s^2