They are all pretty easy all you do is multiply the cost by the amount of things you buy. For example number 4 your variables are cost (c) and songs (s). Your equation is c•s so $0.99 • s. 50 songs would be .99 • 50 which is $49.50
So to find the ratio of the actual house to the house in the picture you would divide 72/4 to get 18. this means that the ratio is 18:1. Now multiply 2.5 x18 to get the real life height of the house. 2.5x18=45.
So the house is 45 feet tall.
Please anyone correct me if I'm wrong but I think this is right.