(a)
Muniya was born on 5 March 2005.
She first sat up on 10 November 2005.
Her age by that time = 5 March 2005 to 4 November 2005 + 6 days of November
= 8 months 6 days
She was 8 months 6 days old when she first sat up.
(b)
Muniya got her first tooth on 15 September 2005.
Her age by that time = 5 March 2005 to 4 September 2005 + 11 days of September
= 6 months 11 days
She was 6 months 11 days old when she got her first tooth.