You would need to buy 175 markers
5 markers (each student gets 5) times 16 (cause there's 16 students in class)=80 markers needed for the first class
5 markers (each student gets 5) times 19 (cause there's 19 students in the class)=95 markers needed for the second class
Add both together 80+95 and u get ur answer which is 175 markers
Hope this helps! :)