Answer :
the given expressions are
j(x)=6x^2-8
k(x)=3x^2-x+7
add both the equation,
[tex]\begin{gathered} j\mleft(x\mright)=6x^2-8 \\ k\mleft(x\mright)=3x^2-x+7 \end{gathered}[/tex][tex]\begin{gathered} (j+k)(x)=6x^2-8+3x^2-x+7 \\ (j+k)(x)=9x^2-x-1 \end{gathered}[/tex]so the answer is 9x^2 - x - 1