You know the triangle has a base of 6 meters, and that the formula to find the area of a triangle is 1/2bh or one-half of the base times the height. So, you would plug in 9 meters squared=one half of six times h, or 9m^2=1/2(6)*(h). In simplifying this, you would get 3h=9m^2. Divide both sides by three and get h=3. Hope this helps, and if you need any further explanations, please let me know!