You set up the equation. Then you do 20 minus 12 which gives you 8. You’re left over with x/3 equals 8. 8 multiplied by 3 gives 24, so x equals 24
L = 4 + w
l/w = 7/5
l = 7w/5
7w/5 = 5 + w
7w = 25 + 5w
2w = 25
w = 12.5
l = 4 + 12.5
l = 16.5
the dimensions are 16.5 x 12.5 cm
