If x was just the number 3, then you would have the equation 3 - 2\*3 = k\*3 - 1. To solve for k, you would add 1 to both sides, then divide both sides by 3.
If x was just the number 2 then you would have the equation 3 - 2\*2 = k\*2 - 1. To solve for k, you would add 1 to both sides, then divide both sides by 2.
The same as if x= 4,-1,pi,... (just not 0, since you can't divide by 0)
The process of how you go about solving it doesn't depend on the particular value of x. That is the essence of algebra. You don't have to know the particular value of x to work with it. You focus on the OPERATIONS.
So to solve 3 - 2\*x = k\*x - 1 for k,
add 1 to both sides of the equation:
4-2\*x = k\*x.
Then divide both sides by x:
(4-2\*x)/x = k