The perimeter of a rectangle is 51cm fin the length and width of the length is twice the width

The perimeter is found by multiply multiplying the length by 2 and adding it to the width multiplied by 2.

Perimeter = 2L + 2W

The length is given as twice the width which would be written as 2W

Now you have P = 2 (2w) + 2w

The perimeter is given as 52 cm:

51 = 2 (2w) + 2W

Simplify:

51 = 4w + 2w

51 = 6w

Divide both sides by 6:

w = 51/6

w = 8.5

The width is 8.5 cm

The length is 2w = 2*8.5 = 17 cm