When talking about a house, if another house is "opposite", it means it's directly across the street.
There's no implication about what the house number of the other house is, only that its location is on the other side of the street.
6879= six thousand eight hundred and seventy-nine[6,8,(79)]
68796879 = sixty eight million, seven hundred and ninety six thousand, eight hundred and seventy-nine**. [68,7(96),8(79)]
It is the Hundred that cause the problem (and) as speech is based on two decimal counts but figures are grouped based on three decimal counts.