From every state you can have 4 transition for each input symbol => 4*4 transition possible for 1 state
There are such 4 states Hence, 4*4 * 4*4 * 4*4 * 4*4 = 4^8 = 2^16
from 4 states we need to select final states so it will be power set of 4 states, so the no. of ways possible = 2^4
Total = 2^16*2^4 = 2^20
A power set includes empty element which denotes number of final state so there is no need to have compulsory final state.