The slope of a line is calculated with the following formula
[tex]\begin{gathered} slope=\frac{y_2-y_1}{x_2-x_1} \\ \end{gathered}[/tex]From our exercise we have the following 2 points
[tex]\begin{gathered} (1,6)\to(x_1,y_1_{}_{}) \\ (2,3)\to(x_2,y_2) \end{gathered}[/tex][tex]slope=\frac{3_{}-6_{}}{2-1_{}}[/tex][tex]\begin{gathered} slope=\frac{-3_{}}{1_{}} \\ slope=-3_{} \end{gathered}[/tex]