Question 798417
"which meets the x axis at x=3", means that this point is on the x axis, so is (3,0).  


The question equivalently asks for the line defined by (9,-3) and (3,0).


{{{y=mx+b}}}, point-slope form.
{{{b=y-mx}}}, and use {{{m=(-3-0)/(9-3)=-(1/2)}}}.
Pick either point to compute b.