You can put this solution on YOUR website! Use A = LW
120 = L(10)
120/10 = L
12 = L
The length is 12 meters.
I will set up the Pythagorean Theorem that you need to find your diagonal.
Keep in mind that the diagonal is the hypotenuse.
Let d = diagonal
(12)^2 + (10)^2 = (d)^2
Can you finish now?