Hey there! I'm happy to help!
Let's call our length and width L and W respectively.
L=1/2W-4
L=18
Since L is equal to 18, we can just replace the L in the first equation with 18 and solve.
1/2W-4=18.
We add 4 to both sides.
1/2W=22
We divide both sides by 1/2.
W=44
Have a wonderful day! :D
