Question 742776
l=w+3 so 
{{{A=lw=(w+3)(w)=w^2+3w}}}


After w is doubled and length is decreased by 4, 
{{{A=(w+3-4)(2w)=(w-1)(2w)=2w^2-2w}}}

Now since the area has not changed

{{{w^2+3w = 2w^2-2w}}}
{{{w^2-w^2+3w-3w = 2w^2-w^2-2w-3w}}}
{{{w^2-5w=0}}}
{{{w(w-5)=0}}}

So width is 0 or 5m

We can discard the 0 solution.

Length is w+3, so length is 8m