The Exorbitant Course Fees -Which Constraint Best Describes the Situation with Decision Variables a Fee

The Exorbitant Course Fees. The $75 per credit hour course fee tacked on to all the MBA classes has generated a windfall of $56,250 in its first semester. "Now we just need to make sure we spend it all," the Assistant Dean cackled. She charged the Graduate Curriculum Committee with generating a shopping list before their next meeting. Four months later, the chairman of the committee distributed the following. As the professor for the quantitative modeling course, he tended to think in terms of decision variables, so he added the left-most column for ease of use.
$$\begin{array} { | c | l | l | l | } \hline \begin{array} { l } \text { Decision } \\\text { Variable }\end{array} & \text { Item } & \text { Cost } & \text { Note } \\\hline \text { A } & \text { iPads for everybody } & \$ 750 / \text { unit } & \text { Must get a cover if these are purchased } \\\hline \text { B } & \text { iPad covers with MBA logo } & \$ 25 / \text { unit } & \text { Not needed unless we buy iPads } \\\hline \text { C } & \text { Speaker series } & \$ 15,000 & \text { Can't afford both this and the iPads } \\\hline \text { D } & \begin{array} { l } \text { Subscriptions to the Wall } \\\text { Street Joumal }\end{array} & \$ 10 / \text { unit } & \text { Don't need if we have the electronic version } \\\hline & \begin{array} { l } \text { Subscriptions to the } \\\text { electronic version of the Wall }\end{array} & & \\\text { E } & \begin{array} { l } \text { Street Joumal }\end{array} &\$5/unit& \text { Worthless without the iPads } \\\hline\end{array}$$
-Which constraint best describes the situation with decision variables A and B?

A) B - A ? 0
B) B - A = 0
C) B + A = 1
D) B + A ? 1