## Thinking Mathematically (6th Edition)

$\frac{y-b}{x}$.
Consider the formula: $y=mx+b$. It is straight line formula for variable m. Now subtract both side by b. \begin{align} & y-b=mx+b-b \\ & y-b=mx \\ & \frac{y-b}{x}=m \\ & m=\frac{y-b}{x} \end{align} Thus, the variable m is$\frac{y-b}{x}$.