Ricco was reviewing the water bill for his carwash business and determined that the highest bill, $$6,000,$ occurred in July when $2,000$ cars were washed. The lowest bill, $$4,500,$ occurred in February when $1,000$ cars were washed. Use the high$-$low method to answer the following questions. What was the variable cost per carwash?$*$$$3\mathrm{.}00$$$1\mathrm{.}50$$$0\mathrm{.}67$$$4\mathrm{.}50$