let's say:
lengh=x
width=y
"The length of a rectangle is 4 inches greater than the width."
That means: x=y+4 (in inches).
the parameter is (by definition) 2*lenght+2*width.
so we have 2*x+2y=24.
we also know that x=y+4
Substituting:
2*(y+4)+2y=24.
2*y+8+2y=24
4*y+8=24//substitute 8 from both sides
4*y=16//dividing both sides by 4.
y=4
So the width is 4!
The lenght is y+4=8!
the dimensions are 4 by 8.
(check: 2*4+2*8=24, correct!)