How Does Distance from Earth's Center Affect Gravity?

[King Khan]

Homework Statement

The force of gravity at Earth's surface on an astronaut if 634N. What is the force of gravity on the same person if the distance is 2m, in multiplies of Earth's radius, from the center of Earth?

Homework Equations

F=Gm1m2/r^2

The Attempt at a Solution

I really don't understand what to plug in where seeing as how they don't even give the mass, if someone could just please help me with this part I could do the rest.

 

[Dale]

Why don't you write it as a ratio of two forces and see if anything cancels.

Fa/Fb

Where Fb is the force at the surface and Fa is the force at twice the radius.

 

[King Khan]

Why don't you write it as a ratio of two forces and see if anything cancels.

Fa/Fb

Where Fb is the force at the surface and Fa is the force at twice the radius.

if you could rephrase that, sorry but I really don't understand.

 

[Dale]

$$F_a=\frac{G \, m1_a \, m2_a}{r_a^2}$$
$$F_b=\frac{G \, m1_b \, m2_b}{r_b^2}$$
Write Fa/Fb, simplify and solve.