Given,
Machine = DFA.
Input alphabats = { a,b}
No. of states = 2 { q0, q1}.
Initial state = q0.
Language accepted = phi.
case-1. When both q0 and q1 are non-final.
Total possible transition at q0 = 2 * 2 { 2 for a and 2 for b}
Total possible transition at q1 = 2 * 2 { 2 for a and 2 for b}
Total possible config. for eqv. DFA = 4 * 4 = 16
case- 2. When q0 - non-final and q1- final.
Total possible transition at q0 = 1 { a and b can not make a trasition to final state q1 other wise accepted language whould not be phi.}
Total possible transition at q1 = 2 * 2 { 2 for a and 2 for b}
Total possible config. for eqv. DFA = 1* 4 = 4.
total No. of possible DFA’s = 16+4 = 20