Idon't understand on how i am suppose to find the valuee

Graph those points given, in a cartesian plane grid,
that is, an x,y axis grid

and try to make a straight line from the leftmost, to
the rightmost, they don't really line up as a straight
line, so... try to draw a line that will cover "most of
the points", there will be a couple or so "outliers",
the line that "covers most of the points" is so-called
"best-fit" line, so, using  that line, try to get what
"y" is, when x = 3

A - age of Abigail
C - age of Cynthia

A = C + 8

A - 20 = 3 (C - 20) 

A - 20 = 3C - 60  

C + 8 - 20 = 3C - 60

C - 12 = 3C - 60                A = C + 8

2C = 48                             A = 24 + 8 

C = 24 years                     A = 32 years