The approximate cost of a 15-ft-by-18-ft rectangular rug is $729.
It costs a family $324 to buy a 10-ft-by-12-ft rectangular rug.
Means for [tex]10\times12=120[/tex] square feet, the cost of rug is $324
So, for 15-ft-by-18-ft or [tex]15\times18=270[/tex] square feet of rug, the cost will be =
[tex]\frac{324}{120}\times270=729[/tex]
Therefore, the approximate cost of a 15-ft-by-18-ft rectangular rug is $729.