In finding the X, please refer to the computation and explanation in this answer:
17-X= 1/3*15+6
17-X= 11
17-11= X
6= X
So, here you get the X by solving the problem on the right first, 1/3*15 will yield 5 and 5 plus 6 will yield 11 then transfer the answer to the left and interchange it with X. So you will now have 17-11= X, and then you will get 6 as the value of X.