On 8th Dec, 2007 Saturday falls. What day of the week was it on 8th Dec, 2006?
The year 2006 is an ordinary year. So, it has 1 odd day.
So, the day on 8th Dec, 2007 will be 1 day beyond the day on 8th Dec, 2006.
But, 8th Dec, 2007 is Saturday.
$\therefore$ 8th Dec, 2006 is Friday.