The synthetic division table is:
$$ \begin{array}{c|rr}-3&8&39\\& & \color{black}{-24} \\ \hline &\color{blue}{8}&\color{orangered}{15} \end{array} $$The solution is:
$$ \frac{ 8x+39 }{ x+3 } = \color{blue}{8} ~+~ \frac{ \color{red}{ 15 } }{ x+3 } $$Step 1 : Write down the coefficients of the dividend into division table. Put the zero from $ x + 3 = 0 $ ( $ x = \color{blue}{ -3 } $ ) at the left.
$$ \begin{array}{c|rr}\color{blue}{-3}&8&39\\& & \\ \hline && \end{array} $$Step 1 : Bring down the leading coefficient to the bottom row.
$$ \begin{array}{c|rr}-3&\color{orangered}{ 8 }&39\\& & \\ \hline &\color{orangered}{8}& \end{array} $$Step 2 : Multiply by the number on the left, and carry the result into the next column: $ \color{blue}{ -3 } \cdot \color{blue}{ 8 } = \color{blue}{ -24 } $.
$$ \begin{array}{c|rr}\color{blue}{-3}&8&39\\& & \color{blue}{-24} \\ \hline &\color{blue}{8}& \end{array} $$Step 3 : Add down last column: $ \color{orangered}{ 39 } + \color{orangered}{ \left( -24 \right) } = \color{orangered}{ 15 } $
$$ \begin{array}{c|rr}-3&8&\color{orangered}{ 39 }\\& & \color{orangered}{-24} \\ \hline &\color{blue}{8}&\color{orangered}{15} \end{array} $$Bottom line represents the quotient $ \color{blue}{ 8 } $ with a remainder of $ \color{red}{ 15 } $.