A domestic removals company received requests from four potential customers about a moving job for a certain day. The revenue from each customer$’$s job and the estimated time needed to finish it are listed below. The company has only one vehicle available for eight hours on that day.

Customer

$1$

$2$

$3$

$4$

Potential revenue $($$$)$

$400$

$300$

$360$

$200$

Time needed $($hours$)$

$4$

$2$

$3$

$1$

Formulate the problem as an integer programming model. Which one is an appropriate definition of the decision variables?