The degree of a polynomial is simply the monomial with a coeficient that has the highest degree.
6x^6 = 6 degree
9x^3 = 3 degree
3x^2 = 2 degree
-4x^10 = 10 degree
-9x^5 = 5 degree
-5x^6 = 6 degree
Because -4x^10 has the highest degree, the degree of this polynomial is 10.
The answer is the fourth one.
400,000 milligrams because 1 gram is 1000 milligram.