A number cube has 6 probable possible sides: 1,2,3,4,5,6. These are all equally probable. The chance of rolling 2 is 1/6, the chance of rolling something other than 2 is 5/6.
If Randy rolls 72 times, we should view the probability out of 72, so we should convert 5/6 like this:
6x12=72 (Possibility)
5x12=60 (Probability)
Your answer:
P(1,3,4,5,6) = 60/72