Hi,
The length of a rectangle is 4cm more than the width
Let x and (x+4cm) represent the width and length respectively
Question states***
P= 2(x+ 4cm) + 2x = 3(x+4cm) + 4cm
x = 8cm, the width
CHECKING our Answer*** length is 12cm (8cm+4cm)
2*12cm + 2*8cm = 40cm = 3*12cm + 4cm = 40cm