Intermediate Algebra (6th Edition)

$h=9$ feet
We know that the area of a triangle can be calculated as $A=.5bh$, where b is the base and h is the height of the triangle. We know that the area is 18 square feet and the base is 4 feet, so we can plug these values into the area formula to solve for h. $18=.5\times4\times h=2h$ Divide both sides by 2. $h=9$ feet