X=-1
The axis of symmetry will be directly in the middle of the intercepts.
Step 1: Find the slope:

This gives you
, but we need to find b.
To find b, substitute in one (x,y) pair and it doesn't matter which one. I'll go with (4,-2):
![\begin{aligned}-2&=-\dfrac{3}{2}(4)+b\\[0.5em]-2&=-6+b\\[0.5em]4&=b\end{aligned}](https://tex.z-dn.net/?f=%5Cbegin%7Baligned%7D-2%26%3D-%5Cdfrac%7B3%7D%7B2%7D%284%29%2Bb%5C%5C%5B0.5em%5D-2%26%3D-6%2Bb%5C%5C%5B0.5em%5D4%26%3Db%5Cend%7Baligned%7D)
Now take that b-value and plug in into the slope-intercept form:

It's always a good idea to toss in the other x-value from the other point, to make sure it checks out.
Answer:
The answer is x = 3 and y = -1
Step-by-step explanation:
If you were to graph the two lines, their equations would be y = x - 4 and y = -x + 2. The two lines intersect at the point (3, -1), so the solution to the system is x = 3 and y = -1.
The mid point is 15 because it is in the middle of 10 and 20