The scatter plot below shows the number of stamps katie collected in different months: what is the approximate predicted number of stamps she collected in the 25th month? 980 990 1000 1010

First, find the slope. locate two corner points to make calculation easier and more accurate. Notice here (1,30) and (4,150) are right on the corner of a unit square.
m=(150-30)/(4-1)=40
the equation of the line is y=40x+b
next, find b by using one of the above two corner points. I'll use (1,30) here.
30=40*1+b
b=-10
It doesn't make sense that the starting number of stamps is negative. Let's just assume Katie owed her friend 10 stamps and let's ignore the negative number.
our equation is y=40x-10
when x is 25, y=40*25-10=990

It would be the second one because it passes the vertical line test