find k in terms of g and R?

Question

the function is a piecewise function:

F(r) =
{ (mgR^2) / r^2 if r >= R
{ mkr if 0 <= r < R

g and k are positive constants and R is the radius of the earth. given that F(r) is continuous, find k in terms of g and R...

no idea where to start...

Answer 1

At R,
mkR = mgR^2) / R^2
k = g / R

Answer 2

m g R²/ R² = m k R (when r = R)
g = k R
k = g / R