you purchase muffins for you and your coworkers. you buy a total of 15 muffins for $27.50. each blueberry (x) costs $1.50, each chocolate chip (y) costs $2, and each banana nut (z) costs $2.50. you know that you will need twice as many blueberry as chocolate chip muffins. how many of each type of muffin did you buy? the system of equations is using the elimination method, group the first two equations together and eliminate the x. what is the resulting equation containing only y and z?