Explain Judging the market value valuations for Acquisition of firms

Shefrin's Chapter 10 (pp 162-163) mentions AT&T's acquisition of NCR. In the five months that followed AT&T's announcement that it planned to acquire NCR, the cumulative abnormal return over the negotiation period for this merger, 11/01/90 - 05/07/91 was -13.33% for AT&T and +120.29% for NCR. At the beginning of this period, AT&T's stock price was $34 and it had 1.092 billion shares outstanding. In contrast, NCR's stock price was $47.25 with 64.5 million shares outstanding.