The digit in the unit place of the number 6^129 × 7^307 is

The unit digit of 6 raised to any positive integer power is always 6, so 6^129 has unit digit 6. For 7^307, the unit digits cycle as 7, 9, 3, 1 with period 4. 307 mod 4 = 3, so unit digit of 7^307 is 3. The unit digit of the product 6 × 3 = 18, which has unit digit 8. Wait — that gives 8, not 2. Let me recheck: 6 × 3 = 18, unit digit is 8. So the answer should be (c) 8. The correct answer is 8.