You can write this as,

Where,

is just a number.

Thus, it is polynomial of degree 3.

A linear function. Not a quadradic. Note E(m) is function of 'm'. And c^2 is a number here. So it is a linear function.2. E(m) = mc^2

Again 'n' has nothing to do with this, look at the x's it is a polynomial is of degree 4.3. g(x) = k(2n)^5 - 2x^3 + 5x^4