In this item, we are given that the number of miles that John runs every day vary. Therefore, it is just rightful that we use three different variables for the number of miles he ran for three days. For the purpose of representation in this item, we let the variables be x, y, and z. The total miles he ran is equal to the sum of the three variables. Let T be the total and that would be equal to,
T = x + y + z