Answer:
10th of June is their mother's birthday
kimberly remembers that her mother's birthday is after 6th but before 11th of june.
- after 6 is 7, before 11 is 10.
her sister sarah remembers that her mothers birthday is before 16th and after 9th of june.
- before 16 is 15, after 9 is 10.
10 are common on both cases