Samsung's mobile communications division uses $20,000$ memory chips per month. Their trucking company charges Samsung $$300$ per shipment, independent of the quantity purchased. The manufacturer of the memory chips offers an all unit quantity discount with a price of $$1$ per memory chip for orders under $18,000$ units, $$0\mathrm{.}96$ per chip for orders between $18,000$ and $36,000$ units $($including $18,000$ and excluding $36,000),$ and $$0\mathrm{.}92$ per chip for orders $36,000$ units and larger. Samsung incurs a holding cost rate of $15\%$ per year. What is the optimal lot size and optimal total cost $($TC$*)$ for Samsung?

B$.$ Q$*=43,000,$ TC$*=$ $$362,293$

C$.$ Q$*=36,000,$ TC$*=$ $$203,518$

D$.$ Q$*=36,000,$ TC$*=$ $$225,284$