When the polynomial has more than one variable you have to sum the exponents of the variables for every monomial. The largest sum is the order of the polynomial.
Here:
momomial sum of the exponents
8x^3y^2 3 + 2 = 5
-10xy 1 + 1 = 2
4x^2y^2 2 + 2 = 4
Then the degree is 5.
