First,12 multiplied by 18 is 216. Multiply 216 by 3.50 to get the amount paid for the living room (Which is $756). Next, you find the square footage of the bedroom (12x12) which is 144 square feet. Multiply 144 by 3.50 and you get the amount paid for the bedroom ($504). Thirdly, you add the cost of the living room and the bedroom together, giving you $1,260 total. Lastly, you divide 504 (Bedroom) by 1,260 (Total) to get .4 . Multiply by 100 (Or just move the decimal twice to the right), and you get your percentage which is 40%