Answer
The student spent 3.64 hours walking.
Work Step by Step
$1 ~day = (24 ~hours)(3600~s/hr) = 86400~s$
Let $t$ be the time in seconds spent walking.
Then the remaining time is (86400 - t) seconds.
$(280~W)~t + (100~W)(86400 - t) = 1.1\times 10^7~J$
$(180~W)~t + (100~W)(86400~s) = 1.1\times 10^7~J$
$t = \frac{1.1\times 10^7~J - 8.64\times 10^6~J}{180~W}$
$t = 13111~s = 3.64~hours$
The student spent 3.64 hours walking.
