Answer
a) $F=5.2\times 10^{-9}N$
b) $r=1.2m$
Work Step by Step
(a) We know that
$F=G\frac{m_1m_2}{r^2}$
We plug in the known values to obtain:
$F=6.67\times 10^{-11}\times\frac{6.1(7.2)}{(0.75)^2}$
$F=5.2\times 10^{-9}N$
(b) As $F=G\frac{m_1m_2}{r^2}$
This can be rearranged as:
$r=\sqrt{\frac{Gm_1m_2}{F}}$
We plug in the known values to obtain:
$r=\sqrt{\frac{6.67\times 10^{-11}(6.1)(7.2)}{2.0\times 10^{-9}}}$
$r=1.2m$
