it costs a family $324 to buy a 10 ft by 12 ft rug. at this rate what will it cost them to buy a 15 ft by 18 ft rug? i divided 10 and 12 by 2 to get 5 and 6. i divided 15 and 18 by 3 and got 5 and 6. what do i do next? 2. hmm i don't know if that'll work. what i would do is set up a proportion. the fractions would be area to price. $\frac{120}{324}=\frac{270}{x}$ See how I got that? Criss-Cross multiply: $87480 = 120x \Rightarrow x = 729$ So the price would be$729.