I'm confused what calculations i am supposed to be using for these problems. What i mean by that is what method or formula am i supposed to use to calculate the answers to the problems and can you walk me through a few of them. (these are some example problems) i can figure out the rest from here if i know how to do these

1) Markson and Sons leases a copy machine with terms that include a fixed fee each month of $500 plus a charge for each copy made. The company uses the high-low method to analyze costs. If Markson paid $360 for 5,000 copies and $280 for 3,000 copies, how much would Markson pay if it made 7,500 copies?

2)Rose Company has a relevant range of production between 10,000 and 25,000 units. The following cost data represents average cost per unit for 15,000 units of production.

Using the cost data from Rose Company, answer the following questions:

A. If 10,000 units are produced, what is the variable cost per unit?

3) If 18,000 units are produced, what is the variable cost per unit?