Hi again! I'm happy to help!
First, we need to know what our terms mean. We have the term midpoint, which means it is in the middle of the line. Since we know that k is in the middle of jl, we know that : 2kl=jl
Since we know the coordinates of k and l, we can find how far they are apart, then double the difference and add it to l.
The x point of l is -8, and the x point of k is -5. This means that they are 3 (positive) units apart, and that j and l will be 6 units apart. (for x)
The y point of l is 6, and the y point of k is 10. This means that they are 4 (positive) units apart, and that j and l will be 8 units apart. (for y)
Now, we know that since k and l are 3 units apart on the x axis, and 4 on the y axis, this means that j and l will be 6 units apart on the x axis, and 8 on the y axis.
Now all we have to do, is add these values to the coordinates of l, and we will have our j coordinates.
(-8,6)
+6 +8
j=(-2,14)
Now, we know that the coordinates of j are (-2,14).
I hope this was helpful, keep learning! :D