A domino consists of two congruent squares placed side by side. The perimeter of the domino is 60 units. What is the area of the domino, in square units?
Suppose that the domino's short side measures $l$ units.  Then it's long side measures $2l$ units, and the domino's total perimeter is $6l = 60$.  Thus $l = 10$ and the domino's area is $10\cdot 20 = \boxed{200}$ square units.