You know what the 4th value has to be 20.

So you have __,__,__,20,__,__,__

Fill the first 3 numbers with the smallest 3 positive integers (1,2,3)

now you have 1,2,3,20,__,__,__

fill the next to numbers after 20 with 21 and 22

1,2,3,20,21,22,x

Since the average formula is ,

put what you know into the formula:

Calculate the maximum value by multiplying 7 by 20 and subtracting 69:

Answer: 71

verify: (120 is max value for equation, calculate by