(a) A number is divisible by 4 if the number formed by its two last digits is divisible by 4

Number formed by last two digits of 4096 = 96

96 is divisible by 4

Hence, 4096 is divisible by 4.

(b) A number is divisible by 4 if the number formed by its two last digits is divisible by 4

Number formed by last two digits of 21084 = 84

84 is divisible by 4

Hence, 21084 is divisible by 4.

(c) A number is divisible by 4 if the number formed by its two last digits is divisible by 4

Number formed by last two digits of 31795012 = 12

12 is divisible by 4

Hence, 31795012 is divisible by 4.