Math exam coming up please help.?

Hey guys, so i have a secondary 3 (grade 9) math exam tomorrow and we are allowed our cheat sheets which is basically a paper where we can jot down notes from the whole year to use during the exam.So i have done mine but I am wondering something to put on it. Basically lets say I have to find the volume of a house which is built up of a rectangular base prism (base) and a rectangular base pyramid (roof), and the question asks something like how much paint will it take to paint the entire house if it costs...14$ for each....100 liters of paint. Now if i say my total volume was 15,789m3, how would i calculate how much it would paint i would need and how much it would cost to purchase that much paint? Sorry if the example is a bit off, this is off the top of my head. But if anyone knows what I'm talking about and could give me a formula or something that would work for this, or even a better example with an answer, please help.