A constant is a polynomial of degree

Write the degree of the polynomials.

$2x^2+x+5$

Write the degree of the polynomials.

$1-2x+x^2-5x^3+x^4$

Write the coefficient of $y^2$ in $-8x{y}^2$

Write the coefficient of $c^2$ in $5ab{c}^2$

Write down the algebraic expression whose terms are: $\frac{1}{2}{x}^2, -\frac{5}{7}xy, 5y^2, 6$

What is the algebraic expression for "two-thirds of $n$ decreased by $4$ times $a$".