Answer
$48000 (cos 36 ^\circ) \approx 38,832$ ft-lb
Work Step by Step
Horizontal component of the force is: $|F|cos 36 ^\circ$
$F=400 lb$
and
$d =1200 ft$
As we know, the work done is calculated as:
$ W=| F||d| cos 36^\circ$
Thus,
$ W=( 400 lb) (120 ft) (cos 36^\circ)$
$W= 48000 (cos 36 ^\circ) \approx 38,832$ ft-lb
