39. How many six-digit numbers are there with the second-to-last digit being 1, which are divisible by 4?
39. It is clear that the numbers divisible by 4 are those and only those numbers whose last two digits form a number divisible by 4. Then, if the second-to-last digit is 1, the last digit can only be 2 or 6. In total, we get $9 \cdot 10 \cdot 10 \cdot 10 \cdot 1 \cdot 2=18000$ required numbers.