Answer:
Mariana takes the two pills together after 18 hours.
Step-by-step explanation:
Mariana must take two pills; one every 6 hours and another every 9 hours.
She take two pills together. Let she takes the two pills together after t hours at the time when she take initially.
To find the time to take the two pills together, take the least common multiple of 6 and 9.
6 = 2 x 3
9 = 3 x 3
So, the least common multiple is 2 x 3 x 3 = 18
So, she takes the two pills together after 18 hours.
