Determine the depth of the gutter

Question

A rain gutter is made from sheets of metal that are 18 inches wide. The edges are turned up to form right angles. Determine the depth of the gutter that will allow a cross-sectional area of 21 square inches. Show that there are two different solutions to the problem. 

Answer 1

Draw and label a diagram!

h represents the height of the gutter

18 - 2h represents the base of the gutter

 

21 = h(18 - 2h)

 

Can you solve for h and answer?