With linear function models for 20 points, you.

Y=mx+b
m=slope
b=yintercept

input points
when x=1
y=1
1=1m+b

and
x=2
y=-2
-2=2m+b
multilpy first equaiton by -1 and add to othe requation

-1=-m-b
-2=2m+b +
-3=m+0b

-3=m
y=-3x+b
1=-3(1)+b
1=-3+b
add 3
4=b
y=-3x+4

first blank is -3
second is 4

We only need two points:
(1,1)
(2,-2)

Point slope form:
Given a point (x₀,y₀) and the slope m, the point -slope form is:

y-y₀=m(x-x₀)

If we wante to find out the slope:
Given two points:
(x₁,y₁)
(x₂,y₂)
The slope is:

m=(y₂-y₁) / (x₂-y₁)

In this case:
(1,1)
(2,-2)

m=(-2-1) / (2-1)=-3

We have a point (1,1) and the slope m=1
The point-slope  form is

y-1=-3(x-1)

y-1=-3x+3
y=-3x+3+1
y=-3x+4

y=-3x+4