#### Answer

Second equation, variable $y.$

#### Work Step by Step

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.