2a = 4 Difference between the difference of the first two terms and the second third terms (the difference between -5 and -3 is 2 the difference between -3 and 3 is 6; the difference between 6 and two is 4)
2a = 4 so a = 2; 3(2) + b = 2 → 6 + b = 2 so b = -4; 2 - 4 + c = -5 → -2 + c = -5 so c = -3