Question 57831
If l=length and w=width, we have two unknowns.  We need two equations to solve for two unknowns.

{{{drawing(300,200,0,10,0,10,rectangle (2,2,8,8), locate (5,1.5,l), locate (8.5,5,w))}}}

The problem gives us both equations:
"The length of a rectangle is 9 in. more than twice its width" ==> {{{l=2w+9}}}
"perimeter of the rectangle is 30 in" ==> {{{2w+2l=30}}}

Plug the first equation into the second:
{{{2w+2(2w+9)=30}}}
Distribute:
{{{2w+4w+18=30}}}
{{{6w=12}}}
{{{highlight(w=2)}}}inches