If 1/6 of the bags of pet food are cat food, then the other 5/6 is other pet food. Since there are 4 bags that make up 1/6 of the food, multiplying 4 by 6 should get the answer. 4 x 6 = 24
y will be the whole cost. 6 is how many sessions you have and x is the cost of each of those sessions. The one time introduction fee is 25. you would add 25 plus 6 times the cost of sessions (x) and you would get your answer (y).