Most of the information's that are required for solving this question is already provided in the question. Based on those details the answer to the question can be easily determined.
Number of different classes taught by Mrs. Sands = 6
Number of students in each class = 36
Then
The total number of students taught by Mrs. Sands = (36 * 6)
= 216
So the total number of students that Mrs. Sands teaches is 216. I hope the procedure is clear enough for you to understand. You can always use this procedure for solving similar problems without requiring any help from outside.