This question is not specific enough.
A monomial is one term. You simply just have to write it out and figure it out. You can add exponents to get the highest degree. The only difference is, that you can't add the polynomials exponents because they aren't in one term. TO GET the highest degree, you add the exponents of ONE TERM. Please check how you get the degree of a monomial, it looks like you don't know how to get the degree.