Surfer Sam Company produced $4,000$ units of product that required $2\mathrm{.}5$ standard hours per unit. The standard fixed overhead cost per unit is $$0\mathrm{.}80$ per hour at $10,400$ hours, which is $100\%$ of normal capacity. What is the fixed factory overhead volume variance?

a$.$ $$(320)$ favorable

b$.$ $$(400)$ favorable

c$.$ $$400$ unfavorable

d$.$ $$320$ unfavorable