Answer:

Explanation:
(Assuming the den is a rectangle)
Let
be the length of the den. Because the length is 10 feet longer than the width, the width of the den can be represented as
.
The area of a rectangle is given as
, therefore we can form the following equation:

Expanding this, we have:

This factors into
, therefore
.
Because -11 is extraneous, the length of the den is
feet and the width is
. Thus, the dimensions of the den are
.