Answer
$6.2~~$ candy bars would supply the required energy.
Work Step by Step
We can find the change in gravitational potential energy from sea level to the summit of Mount Everest:
$\Delta U = U_f-U_0$
$\Delta U = mgh-0$
$\Delta U = (90~kg)(9.8~m/s^2)(8850~m)$
$\Delta U = 7.8\times 10^6~J$
The climber would expend $~~7.8~MJ~~$ of energy.
We can find the number of required candy bars:
$\frac{7.8~MJ}{1.25~MJ} = 6.2$
$6.2~~$ candy bars would supply the required energy.
