The amount of the average investment for a proposed investment of $$173,000$ in a fixed asset with a useful life of $4$ years, straight$-$line depreciation, no residual value, and an expected total income of $$28,500$ for the $4$ years is

a$.$ $$28,500$

b$.$ $$7,125$

c$.$ $$43,250$

d$.$ $$86,500$