Multiply polynomial $ \, \color{blue}{ 3x+6 } \, $ by $ \, \color{orangered}{ 3x+1 }$.

$$ \left( \color{blue}{3x+6} \right) \cdot \left( \color{orangered}{3x+1} \right) = 9x^2+21x+6 $$

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

$$ \begin{aligned} \left( \color{blue}{ 3x+6}\right) \cdot \left( \color{orangered}{ 3x+1}\right) &= \underbrace{ \color{blue}{3x} \cdot \color{orangered}{3x} }_{\text{FIRST}} + \underbrace{ \color{blue}{3x} \cdot \color{orangered}{1} }_{\text{OUTER}} + \underbrace{ \color{blue}{6} \cdot \color{orangered}{3x} }_{\text{INNER}} + \underbrace{ \color{blue}{6} \cdot \color{orangered}{1} }_{\text{LAST}} = \\ &= 9x^2 + 3x + 18x + 6 = \\ &= 9x^2 + 3x + 18x + 6 = \\ &= 9x^2+21x+6; \end{aligned} $$

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