Question 1000584

A landscape architect is planning a new nature area in middle of campus. She wants the length to be twice the width, and wants to put a 3foot high retaining wall around the perimeter.  There will be 300 total feet wall installed.  How wide will this area be? 
I think it's α=l*w
But now I'm lost,  could someone help me? 
<pre>Width of nature area: {{{highlight_green(16&2/3)}}} ft