Answer:
y = -3x + 8
Step-by-step explanation:
You have to find the slope first using the formula 
Insert any two points in the equation (1,5) and (2,2) and you get -3.
Then, you do any x value times the slope (1*-3 = -3) and add so that it equals the corresponding y value (8).
This makes it y = -3x + 8.
The Answer is $9.00 because if you just add 4.50 to 4.50 it is $9:00.
3.1 is like a example when it is hiding a zero behind it and you find this when you do a math problem and you don't put zero in front of a number like 100-89 you don't write "011" so that is why it is like that