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

$$ \begin{aligned} \left( \color{blue}{ 3k-1}\right) \cdot \left( \color{orangered}{ 4k+9}\right) &= \underbrace{ \color{blue}{3k} \cdot \color{orangered}{4k} }_{\text{FIRST}} + \underbrace{ \color{blue}{3k} \cdot \color{orangered}{9} }_{\text{OUTER}} + \underbrace{ \left( \color{blue}{-1} \right) \cdot \color{orangered}{4k} }_{\text{INNER}} + \underbrace{ \left( \color{blue}{-1} \right) \cdot \color{orangered}{9} }_{\text{LAST}} = \\ &= 12k^2 + 27k + \left( -4k\right) + \left( -9\right) = \\ &= 12k^2 + 27k + \left( -4k\right) + \left( -9\right) = \\ &= 12k^2+23k-9; \end{aligned} $$

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