Question 167268
p=2(l+w) where p is the perimeter, l=length,and w=width

l=3w-6  so plugging in the know values {{{36=2((3w-6)+w)}}}
:
{{{36=8w-12}}} {{{8w=48}}} {{{highlight(w=6)}}}width

so length equals {{{highlight(3(6)-6=12)}}}length