Answer
$x=\dfrac{y-y_1+mx_1}{m}$
Work Step by Step
Using the properties of equality, in terms of $x$, the given expression, $
y-y_1=m(x-x_1)
,$ is equivalent to
\begin{array}{l}\require{cancel}
y-y_1=mx-mx_1
\\\\
y-y_1+mx_1=mx
\\\\
\dfrac{y-y_1+mx_1}{m}=\dfrac{m}{m}x
\\\\
x=\dfrac{y-y_1+mx_1}{m}
.\end{array}
