its B.6 because when you plug in 1 for y the equation is 3x-1=17 and you have to cancel out y to get 3x=18 by itself because you have to add 1 to the 17 since you canceled it out of the equation then you are left with 3x=18 and you divide both sides by 3 and then 18 divided by 3 is 6 so x=6
