Let the width (base) be w. Then the height is 4w. The area of this right triangle is then (base)(height)/2, which must equal 18 square meters.
Substituting the base and height:
(w)(4w)=18 square meters
Thus, 4w^2=18 square meters. Solving for w, w^2=18/4, or w=+9 meters. The height is 4 times that: h = 4(9 meters) = 36 meters.