the above 3 questions you can literally type into google and get an answer

"square" foot should hint at you that you need to multiply the two feet measurements. the area of the room is its length times width, and you want the cost per unit area. thus it is x*15.5*10A room is 15.5 feet long by 10 feet wide. Carper costs x per square foot. How much does it cost to carpet the room? (I put x so nobody goes and solves it -.- I just want to know how its done, so please show me how to set it up.)

How do you find the area of a triangle?