Opposite sides equals to 7 and so you add 7 + 7 which equals to 14. Next you subtract 30 by 14 to get the total of the opposite side of L and itself which gets you 16 which is then divided by 2 because you have L and its opposite side which would give you 8. So L equals to 8.
Check:
7 + 7 + 8 + 8
14 + 16
30
