The greatest amount of money that rounds to $150.40 is $150.44, and the least amount is $150.35. This is because if a number is 5 or above, it rounds up. If a number is 4 or less, it rounds down.
It works because 7 x 9 x 10 is the same thing as 7 x 90, since 9 x 10 is just 90. So basically he is just writing more but the answer will still be the same.
