Answer :

Well technicaly speaking wouldnt the width or the length be the height? Depending on what way the object is facing and is and what sides the length and width are applied to. Enjoy!=) 
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