Kendra has a math test every 12 school days and a vocabulary test every 9 school days. she had both a math test and a vocabulary test today. the next time she will have both tests on the same day will be in school days.

So the answer is 36

Step-by-step explanation:

In order to find the next time Kendra will have both tests on the same day, find the least common multiple of each increment of days. Write some multiples of each number, and then find the smallest multiple that both numbers have in common. The smallest multiple that both numbers have in common is 36. Therefore, Kendra will have both tests on the same day again in 36 school days.