Algebra 1: Common Core (15th Edition)

Second equation, variable $y.$
To avoid fractions in the first step (solving one equation for one of the variables) we seek a variable with coefficients 1 or -1. In this case, the variable y in the second equation would be our choice, as its coefficient is $-1.$ $6x-y=1\qquad$ ... add $y-1$ $6x-1=y$ And, in the next step, we would substitute $y$ with $6x-1$ and solve for x.