I think the answer is **12/19**

To get no solutions the variable side must cancel out.

Since the last equation only has variables x and z, we have to cancel the y so

Multiply x+y+3z=10 by 8 to get 8x+8y+24z=80

substract the second equation to get 12x+19z=63

then we have to cancel the z

multiply the last equation by 19 to get 19xz+19z=57

(12x+19z=63)-(19xk+19z=57) to get 12x-19xk=6

the left side of the equation must equal zero, so 12x=19xk

19k=12

divide by 19

**k=12/19**