Let the width be x.
The length will thus be 2x - 3.
Perimeter of rectangle = 42
length + length + width + width = 42
2x - 3 + 2x - 3 + x + x = 42
6x - 6 = 42
6x = 42 + 6
6x = 48
x = 48 / 6
x = 8
When x = 8, we have 2x - 3 = 2(8) - 3 = 16 - 3 = 13
Hence, the dimension of the rectangle is 13 by 8.