12^(n+1)÷4^(n-2) = (3*4)^(n+1)÷4^(n-2) = 3^(n+1)*4^(n+1)÷4^(n-2) = 3^(n+1)*4^3 = 64*3*3^n = 192*3^n = 192*15 = 2880