Answer:
About 54
Explanation:
To work backwards from average, you need to multiply the average by the total number of cases, which is 4, since there are 3 current cases/seasons and you want the 4th.
59 * 4 = 236
You then subtract the total home runs that you know of from 236.
236 - 55 - 58 - 69 = 54
To find average, you are adding to the total and then dividing by the number of groups, which is essentially mean (mean is basically the average).