The standard costs and actual costs for factory overhead for the manufacture of $2,500$ units of actual production are as follows:Standard Costs$3$ hours per unit at $$0\mathrm{.}80$ per hour$3$ hours per unit at $$2\mathrm{.}00$ per hourFixed overhead $($based on $10,000$ hours$)$Variable overheadActual CostsTotal variable cost, $$18,000$Total fixed cost, $$8,000$The fixed factory overhead volume variance isO a$.$ $$2,000$ favorable b$.$ $$2,500$ unfavorableO c$.$ $$2,000$ unfavorable d$$0$