L=W+4, so the entire rectangle is 4W+8 because 2(W+4)+2(W). If the perimeter is at least 48, then 4W+8=48 at the least. So, using simple algebra, we can take 8 away from both sides, making 4W=40. Then, we divide both sides by 4, therefore W=10. This is the width. To find the length, we will just add 4. So, the dimensions are 10x14.