there is likely a number missing in what you said the width was equal, so you may need to plug in a number in the work I provide, if so.
A=x-16
W=x+1 (assuming it just wants any number to be able to be added to the 1)
We first need to use the area formula to setup the problem
A=W*L
area equals width times length
We can divide both sides by W to solve for L and get
A/W=L
from here we can just plug in the given values for area and the width
(x-16)/(x+1)=L
This should answer your question, but the x in the denominator may need replaced if the * in your given width is actually a different value besides x.
