Last two talks of the seminar were mostly on the theoretical parts of the subject. This time, we introduce some computational arguments by using equivalence of parities of the transcendental lattice of K3 surfaces, right after a brief reminding of what was talked on previous two talks to warm up. Then, we will apply this idea to reduce the number of cases and time spent on showing which K3 surfaces of Picard number 18 &19 cover an Enriques surface.