Let there are 12 minterms in a function in which 8 minterms are covered by 2 Essential Prime Implicants. Each of the remaining 4 minterms have 2 Non- Essential Prime Implicants. Then the total number of minimal expressions is Answer is 16. Can anyone provide the solution to this problem.

Find the number of Essential prime implicants present in the K Map of the function f=Σ(2,3,5,7,8,12,13).Here the answer is 2,can anybody explain why it is 2?