Solution
[tex]\begin{gathered} Let\text{ }(x_1,y_1),\text{ }(x_2,y_2) \\ Let\text{ }m=slope \\ m=\frac{y_2-y_1}{x_2-x_1} \end{gathered}[/tex][tex]\begin{gathered} If(-5,-11)=\text{ }(x_1,y_1),then\text{ }x_1=-5,\text{ }y_1=-11 \\ (r,9)=\text{ }(x_2,y_2),then\text{ }x_2=r,\text{ }y_1=9 \end{gathered}[/tex]
Using the Slope formula written above;
[tex]\begin{gathered} 2=\frac{9-(-11)}{r-(-5)} \\ 2=\frac{20}{r+5} \\ Cross\text{ }multiply \\ 2(r+5)=20 \\ Expansion\text{ }of\text{ }bracket \\ 2r+10=20 \\ 2r=20-10 \\ 2r=10 \\ Divide\text{ }both\text{ }sides\text{ }by\text{ }2 \\ \frac{2r}{2}=\frac{10}{5} \\ r=5 \end{gathered}[/tex]
Therefore, the missing co-ordinate r is 5.
