Given two points, we can find the equation of a line using the following formula
[tex]\begin{gathered} (x_1,y_1),(x_2,y_2)\to\text{ two points on the line} \\ y-y_1=\frac{y_2-y_1}{x_2-x_1}(x-x_1) \end{gathered}[/tex]
In our case,
[tex]\begin{gathered} (2,1),(9,9) \\ \Rightarrow y-1=\frac{9-1}{9-2}(x-2) \\ \Rightarrow y-1=\frac{8}{7}(x-2) \\ \Rightarrow y=\frac{8}{7}x-\frac{16}{7}+1 \\ \Rightarrow y=\frac{8}{7}x-\frac{9}{7} \end{gathered}[/tex]
The answer is y=8x/7-9/7
