Question 746423
First note that perimeter is measured in inches, and here is the formula for the perimeter of a rectangle:

{{{

P=2(l+w)
}}}

P=336, l=21


so...


{{{
336=2(21+w)
}}}

divide by 2...


{{{
168=21+w
}}}


w=168-21=147

width is 147 inches


:)