If 21y5 is a multiple of 9, where y is a digit, what is the value of y?

Since the number21y5is a multiple of9.So, the sum of its digits2+1+y+5=8+yis a multiple of9.∴(8+y)is either9or18or ...Sinceyis a digit, so(8+y)must be equal to9.i.e.,8+y=9⇒y=9𕒼=1