Answer:
The common multiple is 18
Step-by-step explanation:
Because 9*2=18 and 18*1=18
First we are going to find the common denominator of both fractions. To do that, we are going to multiply their denominators:

Now we can rewrite our expression using the common denominator:

Finally, we can use the trig identities:

and

to simplify our trig expression:
We can conclude that the correct answer is the fourth one.
The answer is B) There are exactly 4 students with 6 textbooks