Question 26769
You don't have any information explicity giving you l or w, but you can create a system of equations.  Use the definition of the perimeter to give you one equation:
{{{l + w + l + w = 150}}} or:
{{{2l + 2w = 150}}}
The other equation requires you to use the ratio of length & width the problem gives you, that is that it is twice as long as it is wide or in math:
{{{2l = w}}}
Substituting for w in the first equation with 2l from the second equation will allow you to solve it.