How to get "i am 11 years old" from "i am 11 years old 1111111111" using regular expression?

I have been thinking so long...

Update:
come up with a regular expression which would replace 11 to eleven and the test string given to them was "i am 11 years old 1111111111". Now the extra 1111111111 at the end was just a trick to see if their regular expressions was correct. If the regular expression was correct the outcome should be "i am eleven years old 1111111111".