Well this is very simple and I will lay it out for you. First you know that one side measures 38.4 and because its a rectangle you now know that there are 2 sides with that same measurement. So if you double 38.4 you get 76.8 and you subtract 76.8 from 118 and you get 41.2 meaning that the other 2 sides added together are 41.2. So then you take 41.2 and divide it by 2 because they are both going to be equal and you get 20.6. The height is 20.6 miles