You can find the answer easily by graphing the problem. In doing so, you will find the slope (rise over run) to be one over five. This is because you rise one unit, and run five.
I believe the formula to find the height would be h= 2a/b and if you use that formula and plug in the area (21.7) of each triangle as well as the base (6) then you would get a height of 7.2 cm. I hope this is correct! :)
