Answer:
F = 1.25 N
Step-by-step explanation:
The equation to calculate Gravitational Force is
F = G (m1 . m2) / r^2
where G is gravitational constant, m1 and m2 are the mass of the 2 objects.
So, assuming that the G, m1, m2 is constant, the equation will be
F1 .
= F2 .

Therefore,
F2 = F1 .
/

And finally we just need to find F2 by inserting this value
F1 = 5N
r1 = 10m
r2 = 20m
I hope you can understand, let me know if you need more explanation.