The missing blank is 2 because 7+2=9.
One day, Mrs 9 and Mr 7 were expecting a baby in 1 week, so Mrs 9 was getting ready to go to the hospital. The night before the birth, Mrs 9 called Mr 7 to come home because she was feeling SICK SICK SICK!! In half an hour, Mr 7 came home to take Mrs 9 to the hospital. About a day later, Mrs 9 had borned a beautiful baby boy, which they called 2, to match their number problem, 7+2=9! The End!! ~,~. :)