Step 1: First we have to write polynomials in descending order.

$$ \begin{aligned} P(x) &= -2x+6 \\ Q(x) &= -2x+6 \\ \end{aligned} $$

In this example we are multiplying two binomials so FOIL method can be used.

$$ \begin{aligned} \left( \color{blue}{ -2x+6}\right) \cdot \left( \color{orangered}{ -2x+6}\right) &= \underbrace{ \left( \color{blue}{-2x} \right) \cdot \left( \color{orangered}{-2x} \right) }_{\text{FIRST}} + \underbrace{ \left( \color{blue}{-2x} \right) \cdot \color{orangered}{6} }_{\text{OUTER}} + \underbrace{ \color{blue}{6} \cdot \left( \color{orangered}{-2x} \right) }_{\text{INNER}} + \underbrace{ \color{blue}{6} \cdot \color{orangered}{6} }_{\text{LAST}} = \\ &= 4x^2 + \left( -12x\right) + \left( -12x\right) + 36 = \\ &= 4x^2 + \left( -12x\right) + \left( -12x\right) + 36 = \\ &= 4x^2-24x+36; \end{aligned} $$

Polynomial Operations Calculator