We have $S_n$ = $3n^2$ + 5n, where Sn be the sum of n terms. $S_1$ = 3 × 1 + 5 × 1 = 3 + 5 = 8 = $a_1$, $S_2$ = 3 × 4 + 5 × 2 = 12 + 10 = 22 = $a_1 + a_2$ ⇒ 8 + $a_2$ = 22 ⇒ $a_2$ = 14 ∴ d = $a_2 - a_1$ = 14 – 8 = 6 Now, $a_m$ = a + (m – 1)d ⇒ 164 = 8 + (m – 1) × 6 ⇒ $\frac{156}{6}$ = m - 1 ⇒ m = 26 + 1 = 27