Answer
a) $v=2.07\times 10^{-7}m/s$
b) the speed in part(a) will increase by a factor of $\sqrt 2$
Work Step by Step
(a) We can find the required speed as follows:
$K.E_i+U_i=K.E_f+U_f$
$0-G\frac{m^2}{r_i}=2(\frac{1}{2}mv^2)-G\frac{m^2}{r_f}$
$\implies mv^2=GM^2(\frac{1}{r_f}-\frac{1}{r_i})$
This simplifies to:
$v=\sqrt{GM(\frac{1}{r_f}-\frac{1}{r_i})}$
We plug in the known values to obtain:
$v=\sqrt{(6.67\times 10^{-11})(0.148)(\frac{1}{145}-\frac{1}{395})}$
$v=2.07\times 10^{-7}m/s$
(b) Since speed is directly proportional to the square root of the mass (that is $v\propto \sqrt m$), then if the mass is doubled the speed in part(a) will increase by a factor of $\sqrt 2.$