find slope
for
(x1,y1) and (x2,y2), the slope is (y2-y1)/(x2-x1)
so
(3,5) and (6,9)
slope=(9-5)/(6-3)=4/3
the equation of a line that passes through the point (x1,y1) and has a slope of m is
y-y1=m(x-x1)
given
(3,5) and (6,9) and m=4/3
y-5=4/3(x-3) and
y-9=4/3(x-6)
see our options
last one is answer