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.
Answer:
d
Step-by-step explanation:
(7,1)
For sake of convenience, reverse the series, then it would be:
21,19,17.....7
a=21, d = -2,
s(4) = 4/2 (21+15)
s(4)=2(36)
s(4) = 72