Grant is rolling a standard six-sided number die 8 times. how many outcomes are possible?

The first roll has 6 possible outcomes.

For each of those, the second roll has 6 possible outcomes, so there are 6×6 = 6² outcomes for two rolls.

For each of those, the third roll has 6 possible outcomes, so there are 36×6 = 6³ outcomes for three rolls.

The pattern continues, so for 8 rolls, there are 6⁸ = 1,679,616 possible outcomes.