0 * 18 = 0
1 * 25= 25
2 * 15 = 30
3 * 13 = 39
4 * 7 = 28
5 * 2 = 10
Total reboots = 132
Total number of machines = 18 + 25 + 15 + 13 + 7 + 2 = 80

Mean average number of reboots = 132 / 80 = 1.65


Thats if I have understood the question correctly of course!