Question 176865
Rectangle's perimeter
1.{{{P=2L+2W=18}}}
Rectangle's area
2.{{{A=L*W}}}
Use eq. 1 to get W as a function of L.
1.{{{P=2L+2W=18}}}
{{{2W=18-2L}}}
{{{W=9-L}}}
Substitute that expression into eq. 2,
2.{{{A(L)=L*(9-L)}}}
{{{A(L)=9L-L^2}}}