To find the degree of a polynomial with one variable (example y, not xy which is two variables), you only need to find the highest exponent. In this problem the number with the highest exponent is 5y^4. If you isolate the number to just the one variable y^4, our highest exponent is 4. Since you find degree by using the highest exponent, in this case 4, your answer is 4.
The degree of the polynomial above is 4.
Answer = 4