We want to know the probability of not getting homework for two days in a row. We know that the probability of getting math homework on any particular day is 70%, this means that the probability of NOT getting math homework on any particular day is 30%.
We will denote by E the event of not getting homework for two days in a row. Thus, as the probability doesn't change when the days pass, we can multiply the probabilities:
This means that the probability of not getting homework for two days in a row is 9%.