heres the problem
 
 For each of the following fission reactions, determine the identity of the unknown nuclide:  U +  n rightarrow  I +  + 2  n  U +  n rightarrow  Kr +  + 2  n  U +  n rightarrow  Sr +  + 2  n  Tip: Enter the element symbol and then place the cursor before the symbol. Click on the isotope button  in the Tools menu to add the stacked superscript and subscript before the element symbol. Use the right arrow key to navigate between the superscript, subscript, and element symbol.
a) 97 Y 39
 
 b) 140 Ba 56
 
 c) 139 Xe 54