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

$$ \begin{aligned} \left( \color{blue}{ 6x+7}\right) \cdot \left( \color{orangered}{ 6x-7}\right) &= \underbrace{ \color{blue}{6x} \cdot \color{orangered}{6x} }_{\text{FIRST}} + \underbrace{ \color{blue}{6x} \cdot \left( \color{orangered}{-7} \right) }_{\text{OUTER}} + \underbrace{ \color{blue}{7} \cdot \color{orangered}{6x} }_{\text{INNER}} + \underbrace{ \color{blue}{7} \cdot \left( \color{orangered}{-7} \right) }_{\text{LAST}} = \\ &= 36x^2 + \left( -42x\right) + 42x + \left( -49\right) = \\ &= 36x^2 + \left( -42x\right) + 42x + \left( -49\right) = \\ &= 36x^2-49; \end{aligned} $$

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