What Is the Activity Variance for the Variable Manufacturing Costs

What is the activity variance for the variable manufacturing costs? $\begin{array}{|l|r|r|r|r|r|}\hline & \begin{array}{r}\text { Actual } \\\text { Results }\end{array} & \begin{array}{r}\text { Flexible } \\\text { Vudget }\end{array} & \begin{array}{r}\text { Flexible } \\\text { Budget }\end{array} & \begin{array}{r}\text { Variance } \\\text { Activity }\end{array} & \begin{array}{r}\text { Master } \\\text { Budget }\end{array} \\\hline \text { Units } & 13,000 & & ? & 2000 \mathrm{U} & ? \\\hline \text { Sales revenue } & ? & 13,000 \mathrm{~F} & ? & ? & ? \\\hline \begin{array}{l}\text { Less: }\end{array} & & & & \\\hline \begin{array}{l}\text { Variable mfg. } \\\text { Costs }>\end{array} & \$ 87,750 & & \$ 91,000 & ? & \$ 105,000 \\\hline \begin{array}{l}\text { Variable } \\\text { mktgiadm.costs }>\end{array} & ? & \$ 3,250 \cup & ? & \$ 4,000 \mathrm{~F} & 30,000 \\\hline \begin{array}{l}\text { Contribution } \\\text { margin }\end{array} & \$ 52,000 & ? & ? & \$ 6,000 \mathrm{U} & ? \\\hline\end{array}$

A) $4,000.
B) $14,000.
C) $24,000.
D) $34,000.