Let X = {x $\in$ N : 1 $\leq$ x $\leq$ 17} and Y = {ax + b : x $\in$ X and a, b $\in$ R, a > 0}. If mean and variance of elements of Y are 17 and 216 respectively then a + b is equal to :

(1) 7

(2) 9

(3) –7

(4) –27

(1) 7

(2) 9

(3) –7

(4) –27