Tìm n

a) $3^{n+2} - 2^{n+2} + 3^n - {2^n}^{}⋮ 10 ( n > 1)$
b)$3^{n+3} + 2^{n+3} + {3^{n+1}}^{} + {2^{n+2}}^{} ⋮ 6$