12. Two trains, Train A and Train B, weigh a total of 312 tons. Train A is heavier than Train B. The difference in their weights is 170 tons. Use elimination to solve the system of equations to find the weight of each train. a + b = 312 a-b= 170 a + b = 312 a - b = 170​

If 30 lb of rice and 30 lb of potatoes cost ? $27.60? , and 20 lb of rice and 12 lb of potatoes cost ? $15.04? , how much will 10 lb of rice and 50 lb of potatoes? cost?

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.

At a book fair, joe bought 24 books at 3 for $5 and had $2 left. how much money did he have at first?