Total number of students in the class = 36
Number of students wearing blue shirts = (1/6) * 36
= 36/6
= 6
Number of students wearing white shirts = (2/3) * 36
= 2 * 12
= 24
Then
Number of students not wearing blue or white shirts in the class = 36 - (6 + 24)
= 36 - 30
= 6
So 6 students in the class are wearing a shirt other than a blue or a white shirt. I hope the procedure is clear enough for you to understand.