Can someone help me with this, and if you can Explain it.

Answer:
20
Step-by-step explanation:
Since C is the midpoint of BD, BC must be equal to CD. Therefore, we can set the equation:
x+4=3x-10
Solve:
14=2x
x=7
Then we find AC, which is:
2x-5+x+4 = 3x-1
We can plug x in to get:
3*(7)-1=20