If tomorrow is tuesday, today is monday.
A week has 7 days " Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday ".
98 / 7 = 14 ( Remainder = 0)
So you can say that after multiples of 7 days, the day will repeat itself as monday.
Hence after 98 days monday will occur again.
So we calculate after the remainder (0) , the answer is Monday.
Simple Logic = And whatever the remainder obtained is, add that to the day.