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put this solution on YOUR website!Let d = the depth of the gutter and w = its width.
The area of the cross-section can be expressed as:

and this is given as 50 sq.in.
The cross-section however consists of only three sides, d+d+w and the sum of these dimensions is given as 20 in.
So we can write the following:
1)

and
2)
Rewrite equation 1) as

and substitute into equation 2).
2a)

Simplify and solve for d, the depth.
2b)

Rewrite as a quadratic equation in standard form.
2c)

Solve by factoring.
2d)

Apply the zero product rule.
2e)

or

which means that...

The depth of the gutter is 5 inches.