In this example we are multiplying two binomials so FOIL method can be used.
$$ \begin{aligned} \left( \color{blue}{ 3x+7}\right) \cdot \left( \color{orangered}{ 5x-2}\right) &= \underbrace{ \color{blue}{3x} \cdot \color{orangered}{5x} }_{\text{FIRST}} + \underbrace{ \color{blue}{3x} \cdot \left( \color{orangered}{-2} \right) }_{\text{OUTER}} + \underbrace{ \color{blue}{7} \cdot \color{orangered}{5x} }_{\text{INNER}} + \underbrace{ \color{blue}{7} \cdot \left( \color{orangered}{-2} \right) }_{\text{LAST}} = \\ &= 15x^2 + \left( -6x\right) + 35x + \left( -14\right) = \\ &= 15x^2 + \left( -6x\right) + 35x + \left( -14\right) = \\ &= 15x^2+29x-14; \end{aligned} $$