Answer:
m=2
Explanation:
The degree of the polynomial is found by add the exponents on each term together. The highest number is the degree of the polynomial
10x^2 +2x^my -4y
10x^2 is degree 2
2x^m y^1 is m+1 (the y has an implied 1)
-4y is degree 1 (the y has an implied 1)
It says the polynomial has degree 3 so m+1 =3
Subtract 1 from each side
m+1-1 = 3-1
m=2