Answer: (13,-7)
Explanation:
By using the formula

is the coordinates of the midpoint.
For finding the midpoint X variable do:

For finding the midpoint Y variable do:
(you can either keep the parenthesis or take them out. Either way, the answer is the same.
Considering coordinate numbers follow the format: (x,y), you'll simply just substitute the numbers found above into their respective places.
x: 13
y: -7
(13,-7).