Squares of side $x$ cm are cut from the corners of a 20 cm × 12 cm sheet and the sides are folded up into an open box. Its volume is a cubic polynomial in $x$. What is the coefficient of $x^2$?

By number of terms:
- **Monomial**: 1 term (e.g. $5x^3$)
- **Binomial**: 2 terms (e.g. $x^2+3$)
- **Trinomial**: 3 terms (e.g. $x^2+2x+1$)

By degree:
- **Linear** (degree 1): $3x-5$
- **Quadratic** (degree 2): $x^2-4$
- **Cubic** (degree 3): $2x^3+x-1$
- **Biquadratic** (degree 4): $x^4+1$

A polynomial can fit multiple categories. $5x^3$ is both a monomial and a cubic.