What is the degree of each monomial -9

The degree of a monomial is the sum of the exponents of the variables.

For example:

monomial: 257 x^3 y^5 z^21.

The degree is the sum of the exponents of x, y and z, this is 3 + 5 + 21 = 29.

When a monomial is just a number, it means that the exponents of the variables are zero. For example:

- 9 x^0 y^0 z^0 = - 9 * 1 * 1 * 1 = - 9.

This is your case, the monomial -9 has degree 0, which is the option B.

This is too long-standing now get out