$*$Find all the prime implicants for the following Boolean functions, and determine which are essential:

$($a$)F(W,x,Y,Z)=m(0,2,5,7,8,10,12,13,14,15)$

$($b$)F(A,B,C,D)=m(0,2,3,5,7,8,10,11,14,15)$

$($c$)F(A,B,C,D)=m(1,3,4,5,9,10,11,12,13,14,15)$

Please provide a throughtout explanation so that I can understand how to work on these problems myself. Thank you!