Question 915411
w for width, L for length;

L=3w;
and 
2w+2L=32;
and you want to know area, which is wL.


Substitute for L in 2w+2L=32.
{{{2w+2(3w)=32}}}
{{{w+3w=16}}}
{{{4w=16}}}
{{{w=16/4}}}
{{{w=4}}}
Use the now found value for w to compute or evaluate L.
{{{L=3w}}}
{{{L=3*4}}}
{{{L=12}}}
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You now know both w=4 and L=12, and you can compute the area, w*L.