As a rocket moves farther and farther upward from the launch pad, what happens to the strength of earth's gravitational field around the rocket?
a. it gets weaker.
b. it grows stronger.
c. it remains constant.

From my understanding of this, the closer to the core of the earth you are the stronger the gravity is, so it probably gets weaker. 

The answer is 62.5N; Efficiency of the wheel and axle system(e)=80%
Velocity ratio of the system(V.R) = 4
Mechanical Advantage of the system(M.A) = ?
e = M.A/V.R ✖ 100
80% = M.A/4 ✖ 100
Make "M.A" the subject of the formula
M.A = 80/100 ✖ 4
M.A= 3.2
Load on the wheel and axle system (L) =20kg = 200N
Efforts required to lift the Load (E) = ?
M.A = Load/Effort
3.2 = 200/ Effort
Make Effort the subject of the formula
Effort = 200/3.2 = 62.5N
Therefore the Effort to lift a mass of 20kg is 62.5N