M. Aschbacher (1986). Finite Group Theory. Cambridge University Press, Cambridge. GAP groups Algorithms, and Programming. Version 4.4.10, 2007.. I. M. Isaacs (1994). Character Theory of Finite Groups. Dover, New York. A. Saeidi and S. Zandi (2012). The number of conjugacy classes contained in normal subgroups of solvable groups. to appear in Journal of Algebra and its Applications.