Equation of line passing through the points $(x_2,y_2)$ & $(x_1,y_1)$ is
$(y-y_1)=\large\frac{y_2-y_1}{x_2-x_1}$$(x-x_1)$
Hence equation of line will be
$(y-6)=\large\frac{6-3}{1-2}$$(x-1)$
$y-6=-3x+3$
$y+3x=9$
$y=9-3x$
Hence $m=-3,c=9$
Hence (b) is the correct answer.