Need some explanations?

Question

anonymous · Answer

Okay, so I'm not about to give everyone the story of my life, but let's just say I've had a rough year. I'm trying to catch back up on this.

 I've done all of them, but I guessed my way through it, since I didn't understand. If someone can help me understand why the answer is what it is, I would be very grateful.

What is m MKL if m JKM =105?
The answer is 63, but I don't know how the process works to find it.

anonymous · Answer

|dw:1380517243154:dw|
It's a bit messy, but basically, since JKM is 105, and you know that JKL is 42, all you have to do is subtract 42 out of 105. 
MKL + JKL = JKM
X + 42 = 105