Not able to pass test cases

#1

Not able to find out what is the error and why test cases are not passing here is my code : https://ide.codingblocks.com/s/370117

#2

your isvalid function is not right
check this corrected code:

#3

(number_of_students - mid)*extra_coupons I am not able to get this part of isvalid can you please expalin

#4

each student performing bad will give y coupons amt individually so we can include that