$6^2 = 36$
$6^3 = 216$
$6^4 = 1296$
$6^5 = 7776$
$6^6 = 56656$
$6^7 = 279936$

We have a pattern of: 3, 1, 9, 7, 5
i.e. the digits would repeat every 5 terms

3 as ten's digit: $6^2, 6^7, 6^{12}, 6^{17}, ....$
1 as ten's digit: $6^3, 6^8, 6^{13}, 6^{18}, ....$
9 as ten's digit: $6^4, 6^9, 6^{14}, 6^{19}, ....$
7 as ten's digit: $6^5, 6^{10}, 6^{15}, 6^{20}, ....$
5 as ten's digit: $6^6, 6^{11}, 6^{16}, 6^{21}, ....$

Hence, option B