Which algebraic expression is a polynomial with a degree of 5?
3x5 + 8x4y2 – 9x3y3 – 6y5
2xy4 + 4x2y3 – 6x3y2 – 7x4
8y6 + y5 – 5xy3 + 7x2y2 – x3y – 6x4
–6xy5 + 5x2y3 – x3y2 + 2x2y3 – 3xy5

The degree of a polynomial is the highest exponent or sum of exponents of the variables in the individual terms of a polynomial.

Looking at each the polynomial:

3x5 + 8x4y2 – 9x3y3 – 6y5: Degree is 6 (look at the 2nd and 3rd term)

2xy4 + 4x2y3 – 6x3y2 – 7x4: Degree is 5 (look at 1st, 2nd, and 3rd term)

8y6 + y5 – 5xy3 + 7x2y2 – x3y – 6x4: Degree is 6 (look at 1st term)

–6xy5 + 5x2y3 – x3y2 + 2x2y3 – 3xy5: Degree is 6 (look at 1st and last term)

Therefore, the answer is the second option:
2xy4 + 4x2y3 – 6x3y2 – 7x4