The range of that set of numbers (the difference between the highest and lowest number) is 11.
It is: 12 minus 8 = 4
(12 * 8) - (12 + 8) = 96 - 20 = 76
gmt plus 8 or about 12-15 hrs ahead of US depending on your zone in US
12+8+10+12+11+9 = 62
40
13 hours
-8 + 12 = 4
12 + 8 = 20
8 + 12 = 20
It is: 8+(-12) = -4
12 - 8 + 3 + 5 = 12