A contractor was in the business of building storage tanks. The learning rate was $0\mathrm{.}80$ on doubled averages. He broke even on the twelfth unit, which brought the average of all the units to $1,500$ hours per unit with a labor cost of $$18,000$ per unit. What was his profit margin on a contract for $30$ such units? Assume that this was the first contract and that he was paid the same price per storage tank. Give the profit margin in dollars and in percent.