There are 26 student in the class.
because, since 6 is directly opposite of 19. Between 6 and 19 there are 12 number. There should also be 12 number before 6 and after 19. There 5 number before 6 which is 1,2,3,4,5.So add 7 number after 19. lets count, 20,21,22,23,24,25,26,1,2,3,4,5 . Thus there are 26 students.