The width of a rectangle is 2 less than twice its length. If the area of the rectangle is 54 cm, what is the length of the diagonal?

Note: Your answer must be a number. It may not contain any arithmetic operations.

For this i have done:

A = lw

so

54= l ( 2l - 2)

54= (2l^2 - 2l)

54 = 2l ( l -1)

This seems wrong...