[tex]y=mx+b\\\\m=\dfrac{y_2-y_1}{x_2-x_1}[/tex]
We have:
[tex](1,\ 5)\to x_1=1,\ y_1=5\\(2,\ 2)\to x_2=2,\ y_2=2[/tex]
Susbstitute:
[tex]m=\dfrac{2-5}{2-1}=\dfrac{-3}{1}=-3[/tex]
[tex]y=-3x+b[/tex]
Susbtitute the coordinates of the point (2, 2) to the equation:
[tex]2=(-3)(2)+b\\\\2=-6+b\ \ \ \ |+6\\\\b=8[/tex]
Answer: y = -3x + 8
