The length of a rectangle is 4 units greater than its width, and the area of the rectangle can be expressed by the eqaution y = x2 + 4x. what is a reasonable domain for this function?

When talking about object measurements, we usually require they be positive.

A suitable domain is x > 0.
(and somewhat less than any substantial fraction of the Earth's dimensions. The numerical value will depend on the chosen units.)

The correct answer is 10%