First what you would do is to make everything it's own area. We know the areas of the two smaller legs are 8m x 5m because we can isolate them from the rest of the block, so the two legs are 40m^2. For the bigger area, all you have to do is subtract 8 from 15 to get the size of the side, which is 7. So now multiply 12m by 7m, which is 84m^2. Finally, just add the two areas together and you get our final answer of 124m^2.