Question 976555
Made more general,
The width (w) of a rectangle is k less than n/d of its length (L). If  the perimeter is p cm. identify the equation of the problem.


{{{2w+2L=p}}}


Description means {{{w=-k+(n/d)L}}}  or  {{{w=(n/d)L-k}}}.


Returning to the perimeter equation and substituting for w,
{{{2((n/d)L-k)+2L=p}}}


{{{2nL/d-2k+2L=p}}}


{{{2nL/d+2L-2k=p}}}


{{{(2n/d+2)L-2k=p}}}-----this may be one of your choices if keeping completely in symbolic form.  


You can solve the equation for L, one of the unknown quantities.
-
{{{(2n/d+2)L=p+2k}}}


{{{((2n+2d)/d)L=p+2k}}}


{{{highlight_green(L=(p+2k)(d/(2n+2d)))}}}


That form for L might be fairly convenient to use.  You can substitute as variables were assigned:
{{{system(n=1,d=3,p=116,k=2)}}};
Evaluate L...