-3x^2 * y^(m+1) + x^3 * y - 3x^4 - 1 是5次4项式 => x^2 * y^(m+1) 是 5次项,m = 2
3 x^(3n) * y^(3-m) * z 是5次项 => 3n + 3 - m + 1 = 3n+2 = 5 => n=1
m = 2,n = 1