If this problem is for a basic algebra class, then you will want to do something like this:
let x = width
then x+5 = length
The area (length times width) is 14:
It's a quadratic equation; get everything on one side and solve by factoring:
or
x = -7 makes no sense in the problem, so reject it; the solution is
width = x = 2
length = x+5 = 7
While that is a good exercise in algebra, note that the formal algebra doesn't help you solve the problem, because in factoring you need to find two numbers whose difference is 5 and whose sum is 14 -- but that's what the original problem required you to do.