A company produces two kinds of septic tanks: type A and type B. Each type B tank takes twice as long to produce as a type A tank. If it only produced type A tanks, the company has the time to produce a maximum of 2000 tanks per week. The supply of materials is sufficient to produce 1200 tanks per week (including both types A and B). Each type B tank requires a special fixture and there are only 900 of these fixtures available per week. At current prices the company makes a profit of $300 for each type A tank and $500 for each type B tank. How many tanks of each type should the company produce to maximize total profit at the current prices? What constraint(s) are limiting the solution?