Here you go, i added a bit of explanation as to why i used the numbers to help you understand the method :)
<u>Answer:</u>
<u>Step-by-step explanation:</u>
The sum of interior angles of a quadrilateral is 360°.
If we consider the measure of one of the unknown angles to be
°, we can set up the following equation:

Now we can solve for
:
⇒ 
⇒
[subtracting 192° from both sides]
⇒ 
⇒
[dividing both sides by 2]
⇒ 
Therefore, the other two angles each have a measure of 84°.
let
A(3,20) B(8,35)
step 1
find the slope AB
m=(y2-y1)/(x2-x1)-------> m=(35-20)/(8-3)------> m=15/5-----> m=3
step 2
with m=3 and the point A(3,20) find the equation of the line
y-y1=m*(x-x1)------> y-20=3*(x-3)----> y=3x-9+20------> y=3x+11
therefore
the answer is
the equation of the line of best fit for Maggie's data is
y=3x+11