Since length is 3 more than the width, you can say that l= w + 3.
Part A) Area is length time width, so you would get (w + 3) × w this can be simplified to w²+3w
Part B) Perimeter is all of the sides added together, or 2l+ 2w. This gets you 2(w +3) + 2w, and this can be simplified to 4w+6
If you need any further explanation, just let me know :)