Chapter 7 - Review - Page 470: 155

$\left( 4,16 \right)$

Using the Midpoint Formula, $\left( \dfrac{x_1+x_2}{2},\dfrac{y_1+y_2}{2} \right)$, the midpoint of the two given points is \begin{array}{l} \left( \dfrac{-3+11}{2},\dfrac{8+24}{2} \right) \\\\= \left( 4,16 \right) .\end{array}