Linear programming-using the simplex method to minimize c

Question

Problem:

Linear Programming : Using the Simplex Method to Minimize C

In this problem I am trying to get rid of the artificial variable using the two phase method. However all of the rows either have negatives or zeros and my final answer keeps coming out to be a negative and none of the other answers plug into the constraints. The problem is
Using Simplex method minimize C:

C=15x₁+12x₂
Subject to 3x₁+x₂>18
x₁+2x₂<12
x₁+x₂=10

The numbers behind the x's are the sub numbers(x sub 1, x sub2, etc...)

The greater than and less than signs are also equal to(the 1st constraint is greater than or equal to)
My final answer for c = 144