Completing the Square Word Problem

Alright I'm not exactly sure what category this question falls under, but it was a question part of a "completing the square" unit.

A rectangle is 6m longer than wide. The diagonal is 30m. Find the dimensions of the rectangle.

I drew a diagram, L representing Length and W representing Width.

(w)^2+(w+6)^2=(30)^2

w^2+w^2+36=900

w^2+w^2=900-36

2w^2=864

w^2=432

w=sqrt 432

w=20.8m

Then I subbed w=20.8m into L = W +6 to find L.

L = 26.8M

So the dimensions were 20.8m and 26.8m. For some reason this doesn't look right. No completing the square was involved in this question. Is my answer correct?