What is the degree of the polynomial a4 + b3 - 2ab + c?

For this case we have a polynomial of two variables.
 The variables of the polynomial are:
 variable 1: a
 variable 2: b
 The degree of the polynomial, in this case, is given by the term of the polynomial that has the highest exponent.
 We then have the following polynomial:
 
 The term with the greatest exponent is:
 
 Therefore, the polynomial is of degree 4.
 
 The polynomial is of degree 4.