area=legnth times width
normally you would subsiutte legnth for height when solving for the area of a triangle
if you have legnth, witdth, and height, then you have volume like volume of a fish tank
so
area=legnth times width
if you meant volume then if you have the area then
area=legnth times width
volume=legnth times width times height
so to solve for height when you know volume, area, legnth , width, then
divide both sides by (legnth times width or area)
volume/(legnth times width)=height