ANSWER:
[tex]B(6,-8)[/tex]
STEP-BY-STEP EXPLANATION:
The first thing is to represent the situation as follows
To calculate the value of B we have the following formula for the midpoint:
[tex]\begin{gathered} (M_1,M_2)=(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2}) \\ M_1=\frac{x_1+x_2}{2} \\ M_2=\frac{y_1+y_2}{2} \end{gathered}[/tex]
replacing and solving in each case:
[tex]\begin{gathered} 7=\frac{8+x_2}{2}\rightarrow x_2=7\cdot2-8\rightarrow x_2=6 \\ -7=\frac{-6+y_2}{2}\rightarrow y_2=-7\cdot2+8\rightarrow y_2_{}=-8 \\ B(6,-8) \end{gathered}[/tex]
