Answer
a) $\sqrt \frac{hG}{c^{5}}$
b) $1.3\times10^{-43}s$
Work Step by Step
a) Through trial and error, we find that the combination of G,c and h that has dimensions of time is $\sqrt \frac{hG}{c^{5}}$
b) Calculating the time of the same =
$\sqrt \frac{hG}{c^{5}}=\sqrt \frac{(6.6\times10^{-34})\times (6.7\times10^{-11})}{3.8\times10^{8}}=1.3\times10^{-43}s$
