The area of a parallelogram is b*h. If you were stuck at the bottom then you didn’t need it in the first place. The 6m at the top is you base, and the 7m is your height. 6*7 equals 42.
If you would want a more technical reason why then you move the right triangle made from the height and put it directly across to where you put it where the other hypotenuse would be. It would then become a rectangle with length as 6 and height as 7.
