find the slope first
slope=(2-1)/(-1+3)=1/4=.25
now use the slope and either point to write in point slope form
y-1=.25(x-2)
y-1=¼x-½
to rationalize all the denominators multiply by the last common multiple, here we get 4
4y-4=x-2
then put in the correct order
x-4y=-2
