Answer:
22
Step-by-step explanation:
The diagonals are divided into 2 parts. They're both equal to each other in order to equal the total length.
Setting them up to equal each other is the easiest way to solve.
2x + 18 = x + 40.
Now with simple algebra, we can find the sidelength of x.
Subtract both sides by x.
x + 18 = 40
Subtract both sides by 18.
x = 22.
