Answer:
20
Step-by-step explanation:
We're king of shown that it's a parallelogram, so we should assume LM = KN (we can't solve it if we don't know if it's a parallelogram).
LM = KN
3x - 4 = x + 12
2x = 16
x = 8
LM = x + 12 = 8 + 12 = 20
KN = 3x - 4 = 3*8 - 4 = 24 - 4 = 20
checks out
