Answer
(a) Negative
(b) $-7.8KJ$
Work Step by Step
(a) As the force acts in the opposite direction to that of motion, the work done is negative.
(b) We know that
$W=Fdcos\theta$
We plug in the known values to obtain:
$W=(120)(65)cos180^{\circ}$
$W=-7800J$
$W=-7.8KJ$