If it was Sunday on 5th January, 1986, what was the day of the week on 14th January, 1993?

On 5 th January, 1986, it was Sunday. 1986 was not a leap year.
The number of odd days in a non-leap year is '1'.
The number of odd days in a leap year is '2'.
So, number of odd days from 5 th January, 1986 to 5 th January, 1993 = (1 + 1 + 2 + 1 + 1 + 1 + 2) days = 9 days
The number of days from 5 th January, 1993 to 14 th January, 1993 = 9 days

The days of the week repeat itself after 7 days, so, (18÷7) , we get 4 as remainder.
So, number of odd days = 4
As, it was it was Sunday on 5 th January, 1986, so, 4 th day after Sunday is Thursday.
Therefore, on 14 th January, 1993, it was Thursday.