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

$$ \begin{aligned} P(x) &= -64x^2+9 \\ Q(x) &= 2x+5 \\ \end{aligned} $$

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

$$ \begin{aligned} \left( \color{blue}{ -64x^2+9}\right) \cdot \left( \color{orangered}{ 2x+5}\right) &= \underbrace{ \left( \color{blue}{-64x^2} \right) \cdot \color{orangered}{2x} }_{\text{FIRST}} + \underbrace{ \left( \color{blue}{-64x^2} \right) \cdot \color{orangered}{5} }_{\text{OUTER}} + \underbrace{ \color{blue}{9} \cdot \color{orangered}{2x} }_{\text{INNER}} + \underbrace{ \color{blue}{9} \cdot \color{orangered}{5} }_{\text{LAST}} = \\ &= -128x^3 + \left( -320x^2\right) + 18x + 45 = \\ &= -128x^3 + \left( -320x^2\right) + 18x + 45 = \\ &= -128x^3-320x^2+18x+45; \end{aligned} $$

Polynomial Operations Calculator