Finding the mass of two planets

[prlion16]

Ok well, I have used up 2 out of 3 of my submissions for this question. I have tried to do a system of equations and failed twice. I really don't even know where to start so I was hoping that you guys could help me.
The problem is.
The mass of a robot is 5720 kg. This robot weighs 3720 N more on planet A than it does on planet B. Both planets have the same radius of 1.33x10^7 m. What is the difference MA - MB in the masses of these planets?

Thank you.

 

[neutrino]

Use the definition of weight. Assume that it's evaluated at the surface of the planets.

 

[prlion16]

ok... I still don't get what I am supposed to do. Sorry. I get that weight is going to be calculated at the surface of the planets so d=1.33x10^7. I got the equation F=6.67x10^-11(5720m1/((1.33x10^7)^2)). I really just don't get what I am supposed to do after this.

 

[neutrino]

You are provided with the difference in weight (of the robot), right?

 

[prlion16]

For planet B it is 5720a and Planet A is 5720a+3720. right?

 

[neutrino]

W_A - W_B = Gm(M_A-M_B)/d²