Adena has a number cube whose sides are labeled 1 through 6. she rolls the number cube three times.

what is the probability that adena will roll 2, then 3, and then 4?

it has to be a

On the first roll, the probability of rolling a 2 is 1/6. On the second roll the probability of rolling a 3 is also 1/6, and the probability of rolling a 4 on the third roll is, you guessed it, 1/6. Therefore the required probability is given by:
1/6 x 1/6 x 1/6 = 1/216