How to diaplay Field A value to Field B in infopath

Question

i have a infopath form. In that i have created two fiels:

 

1. City field (Drop-Down)

 

2. B Field (TextField)

 

If i select "Others" options from City field (Drop-Down) then B Field (TextField) appear to allow enter city name.

 

i am trying B Field (TextField) value display in City field instead of "Others"

 

Thanks