The variation of K is what is found in front of X
W=15 no
W= 21 no
W= 1 Yes
If im right the question is just asking which variable is less than 15.
so the only variable that is less than 15 is 1.
For this case we have the following system of equations:

From the first equation we have:

We substitute in the second equation:

We subtract 5 from both sides of the equation:

We divide -2 on both sides of the equation:

So:

So, the system solution is: 
Answer:
See attached image 