If I were you, I would make the starting point (3,-6). From there, you will want to use the slope of -1/2 (go down 1 unit and to the right 2 units and draw a point)
You are adding 2 each time.
You are trying to find the 30th term, in which 4 are shown.
Subtract 4 from 30
30 - 4 = 26
Multiply 26 with 2
26 x 2 = 52
Add 52 to the last number given (0)
0 + 52 = 52
52 is your answer
hope this helps
