P = perimeter = 42 cm

W = width

L = length

Conditions:

W = 3 + L

Therefore:

P = 2W + 2L

42 = 2(3 + L) + 2L

42 = 6 + 2L + 2L

4L = 36

L = 9

W = 3 + 9

W = 12

By Checking:

P = 2W + 2L

P = 2(12) + 2(9)

P = 42 cm

If the width is w and the length is h, then:

2(h + w) = 42cm

h + w = 21cm.

fact: (h+3)=w

fact: (h+3)+w=21

take the 21 cm from above and divide by 2 (to get the square)

the answer is 10.5 cm. also, take the difference of 3 cm and divide it by two; the answer is 1.5. If you add 1.5 to the 10.5, you get 12 cm for the (w) and if you subtract 1.5 from the 10.5 you get 9 cm for the (h). The rectangle now has a width of 3 cm more than the length and a perimeter of 42 cm.

2h+2w=42

18+24=42

all combos for 21 are possible answers

1,20

2,19

3,18

etc.

If you have to consider ALL possibilities, the list is infinite

I realize that your entire question did not show up initially….The correct combo is 12 and 9…width is 12, length is 9 according to the rest of the problem….

2(h + w) = 42cm

h + w = 21cm.

You need a bit more information to get the length and width.