Help with homework plsss ;;;(((

A)A bag contains m white balls and 3 black balls, balls are drawn one by one without replacement till all the balls are drawn, show that the procedure for drawing balls will come to an end by the nth draw and also find the probability of it coming to an end by the nth draw.

B)The chance of success in each try is P , if Pk is the probability that these are even number of success in k independent trials , find Pk.

I solved but i think i did wrong , plss help ;;((