Digital logic design: k-map finding essential prime implicants

Question

F(w,x,y,z)= wy+ xy+ w'xyz + w'x'y + xz + x'y'z'
which one of the following is the complete set of essential prime imlicants?
1- w, y, xz , x'z'
2- w,y, xz
3- y, x'y'z'
4- y, xz ,x'z'

Here is my solution:-

i created the k-map of bolean function f(w,x,y,z) and here are the minterms of the function f

f(w,x,y,z)= Σm(0,2,3,5,6,7,8,9,10,11,13,14,15)
and here are minterms of product in the function f(w,x,y,z)

wy=(10,11,14,15), xy= (6,7,14,15), w'xyz=(7), w'x'y=(2,3) xz=(5,7,13,15), x'y'z'=(0,8)
and i don't know what to do next. And i know what is essential prime implicant and prime implicants.

Comments

Duplicate of: https://ec.gateoverflow.in/368/gate-ece-2014-set-1-question-41 

Answer 1

Source: https://cse.sc.edu/~hoskinsw/classes/csce211/LecturesF15/Lecture8.pdf

Prime Implicant: A prime implicant is an implicant that (from the point of view of the map) is not fully contained within any one other implicant.

Essential Prime Implicant: An essential prime implicant is a prime implicant that includes at least one 1 that is not in any other prime implicant.

Source: https://ec.gateoverflow.in/368/gate-ece-2014-set-1-question-41

Answer 2

Ans - 4