Answer
b) $5.5 \ km/s$
Work Step by Step
We use the equation for escape speed to find:
$V_{esc} =\sqrt{\frac{2GM}{r}}$
$V_{esc} =\sqrt{\frac{2(6.67\times10^{-11})(5.97\times10^{24})}{6.37\times10^6+(20.2\times10^6)}}=5470\ m/s = 5.5 \ km/s$
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