Answer
Please see the work below.
Work Step by Step
We know that
$U=mgh$
We plug in the known values to obtain:
$U=(8.5\times 10^9)(9.8)(140)=1.166\times 10^{13}J$
We can find the electricity as
$E=Pt$
We plug in the known values to obtain:
$E=(330\times 10^6)(8.0\times 3600)=9.504\times 10^{12}J$
The efficiency is given as:
$\epsilon=\frac{E}{U}\times 100=\frac{9.504\times 10^{12}}{1.166\times 10^{13}}\times 100=81\%$
