The equation of the line passing through [tex](x_1,y_1)[/tex] and [tex](x_2,y_2)[/tex] is given by
[tex]\dfrac{x-x_1}{x_2-x_1}=\dfrac{y-y_1}{y_2-y_1}[/tex]
In your case, the points are (1,4) and (2,2). Plug these values in the equation to get
[tex]\dfrac{x-1}{2-1}=\dfrac{y-4}{2-4} \iff x-1=\dfrac{4-y}{2}[/tex]
We can rewrite the equation as
[tex]2(x-1)=4-y \iff 2x-2=4-y \iff y=-2x+6[/tex]
