Pre-populate content from one text box into another text box

I am sure this is possible but I haven't a clue how to make it happen

I am looping X number of times and the user will be entering a fromValue to a ToValue

LOOP
1.) fromValue to ToValue
2.) fromValue to ToValue
3.) fromValue to ToValue
4.) fromValue to ToValue

what I need to do is when the user enter a ToValue
is for the next fromValue to display the previous ToValue.

Example: user enters
1.) 0 25 in Number 2, the fromValue should be 25.

Thanks for any assistance.