$-\frac{ 6 }{ {x}^{2}-16 }-\frac{ 9 }{ 16-{x}^{2} }$
Factor out the negative sign from the expression and reorder the terms$-\frac{ 6 }{ {x}^{2}-16 }-\frac{ 9 }{ -\left( {x}^{2}-16 \right) }$
Determine the sign of the fraction$-\frac{ 6 }{ {x}^{2}-16 }+\frac{ 9 }{ {x}^{2}-16 }$
Write all numerators above the common denominator$\frac{ 3 }{ {x}^{2}-16 }$