Since we are summing two expressions, we can take away the parenthesis.
So,
[tex]\begin{gathered} \mleft(7x+6\mright)+\mleft(-8x+4\mright) \\ =7x+6-8x+4 \end{gathered}[/tex]Now, we add like terms (add/subtract x's and add/subtract numbers). Let's re-arrange the expression and do the addition/subtraction:
[tex]\begin{gathered} 7x+6-8x+4 \\ =7x-8x+6+4 \\ =-x+10 \end{gathered}[/tex]The sum of the two expression is:
[tex]-x+10[/tex]