Question 519361
l= length
w= width

{{{l=3w}}}
{{{2l+2w=168}}}
Substitute
{{{2(3w)+2w=168}}}
{{{6w+2w=168}}}
{{{8w=168}}}
{{{w=21}}}
Re-Enter
{{{l=3(21)}}
{{{l=63}}}

Length = 63 and Width = 21