Answer
The change in potential energy is $2.9\times 10^6~J$
Work Step by Step
Note that the summit of Mount Whitney is 4505 meters higher than the floor of Death Valley. The height of the hiker increases by 4505 meters when moving from the floor of Death Valley to the summit of Mount Whitney.
We can find the change in potential energy.
$\Delta PE = mg~\Delta h$
$\Delta PE = (65~kg)(9.80~m/s^2)(4505~m)$
$\Delta PE = 2.9\times 10^6~J$
The change in potential energy is $2.9\times 10^6~J$
