Answer:
0 (option a)
Explanation:
for a number to be divisible by 5, it has to end with the digits 0 or 5. for a number to be divisible by 3, the sum of all its digits has to be divisible by 3.
for 63215: 6 + 3 + 2 + 1 + 5 = 17 (not divisible by 3)
for 63210: 6 + 3 + 2 + 1 + 0 = 12 (divisible by 3)
thus, the missing digit is 0.
i hope this helps! :D
