Question 743347
Length and width assigning not really important except to be consistant with how assigned and used.


Taking either dimension as L for "length" and then W for width,
The whole rectangle is as {{{2(L+W)=420}}}.


You could then choose fencing costs of 17*L and 2*8W, so this combined cost for those THREE sides would be {{{17L+16W=3470}}}.


The system based on that is:
{{{2(L+W)=420}}} and {{{17L+16W=3470}}}.


Solving the perimeter equation for W and substituting into the cost equation gives (try doing this on your own) {{{highlight(L=110)}}} feet.
Using this in the formula used for W gives {{{highlight(W=100)}}} feet.