Changing sides of a square (area and derivatives)

How fast are the sides of a square changing at the instant when its sides are 6 feet long and its area is decreasing at a rate of 2 square feet per second?

I assume that the square is on a graph. Then I listed the known variables, which are:

$\displaystyle x=6$

$\displaystyle y=6$

Since area is decreasing at a rate of 2 sq. ft/s, would $\displaystyle x'=-2$? Would I have to find the derivative of the formula Area$\displaystyle =lw$ to help get the answer?