The amount of the average investment for a proposed investment of $$105,000$ in a fixed asset with a useful life of $4$ years, straight$-$line depreciation, no residual value,

and an expected total income of $$28,400$ for the $4$ years is

a$.$ $$7,100$

b$.$ $$28,400$

c$.$ $$26,250,$

d$.$ $$52,500$