Answer
The radius of the orbit is $6.71\times 10^7~m$
Work Step by Step
The period of the satellite's orbit is 48 hours. We can convert the period $T$ to units of seconds.
$T = (48~hrs)(3600~s/hr)$
$T = 172,800~s$
We can use the orbital period and the mass of the earth $M_e$ to find the orbital radius $R$.
$T^2 = \frac{4\pi^2~R^3}{G~M_e}$
$R^3 = \frac{G~M_e~T^2}{4\pi^2}$
$R = (\frac{G~M_e~T^2}{4\pi^2})^{1/3}$
$R = (\frac{(6.67\times 10^{-11}~m^3/kg~s^2)(5.98\times 10^{24}~kg)(172,800~s)^2}{4\pi^2})^{1/3}$
$R = 6.71\times 10^7~m$
The radius of the orbit is $6.71\times 10^7~m$
