The houses have number multiple of 6.
In order to determine two houses with numbers between 70 and 80, list multiples of 6 until the first number over 80, just as follow:
6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84
as you can notice, there are two numbers multiple of 6 in between numbers 70 and 80.
Hence, the answer is houses with numbers 72 and 78.
