Question 1105764
If W is width, the length of the rectangular region is in variable L in equation  {{{2W+2L=18}}}, and area is {{{A=WL}}}.



From the perimeter,
{{{W+L=9}}}
{{{L=9-W}}}



Substituting into A equation,
{{{A=W(9-W)}}}



{{{system(A=W(9-W),or,A=-W^2+9W)}}}