If you have the Forms Builder installed, you can simply go to HELP -> ABOUT FORM BUILDER. This will show separate version numbers for different components. Look for “Forms [xx bits] version…”.
If you have just the runtime, you will need to right-click the runtime executable (usually called ifrunXX.exe, and usually under <oracle_home>\bin), click on “Properties”, select the “Version” tab, and select “File Version” from the item names list.
Hope this helps.