the complete question in the attached figure
Let
w --------> represent the number of weeks that Jack saves
s --------- > represent the total amount saved, in dollars
step 1
find the equation of the line
points
(2,12) and (4,24)
slope m=(s2-s1)/(w2-w1)------->m=(24-12)/(4-2)-----> m=6
step 2
with m=6 and point (2,12)
s-s1=m*(w-w1)--------> s-12=6*(w-2)-----> s=6w-12+12-----> s=6w
the answer is
s=6w