What must be done to the following half-reactions before they can be added together? mn (s) → mn 2+ (aq) + 2e − fe 3+ (aq) + 3e − → fe (s)double the mn half-reaction and triple the fe half-reaction. add h+ ions to the left-side of the mn reaction. triple the mn half-reaction and double the fe half-reaction. double the mn half-reaction. none of the above