Hi! I'm happy to help!
Our total line is JL (4x), and it is split into two parts: JK, and KL. We have our values, and we know that JK+KL=JL, so we can substitute our values and solve for x:
4x=(2x+3)+(x)
4x=3x+3
To solve for x, we have to isolate it on one side of the equation.
First, let's subtract 3x from both sides so that we can isolate x:
4x=3x+3
-3x -3x
x=3
So, our x=3, which means that KL=3.
I hope this was helpful, keep learning! :D