You can write an equation.
KL+LM=KM
Enter the info
x+.5+3x-2=3x+1.5
Combine like terms
4x-1.5=3x+1.5
Add 1.5 to both sides
4x-1.5+1.5=3x+1.5+1.5
4x=3x+3
Subtract 3x from both sides
4x-3x=3x+3-3x
x=3
Then, enter 3 into the expression to find LM
3x-2
3(3)-2
9-2
7
LM is worth 7.
I hope this helped!