Ok so heres the problem. my brain hurts. plzzz me with this math problem

Oh Foxy, Foxy, how totally debilitated you must be !  Try to relax.  Nobody
enjoys a painful brain, and believe me, this problem is not worth it.

Let me put it to you this way:  What if the problem said . . .

-- Demarcus has $8 more than his sister.
-- His sister has $4.
-- How much money ' M ' does Demarcus have ?

If your brain didn't hurt, you could quickly solve this right in there.
You would know that Demarcus' money ' M ' = 8 + 4 .

That's almost exactly what the problem does say. 
Except it doesn't say he has "$8 more than his sister",
it says he has "at least" that much.
So you know that ' M ' is not exactly = 8 + 4, but that's the least it could be.
The actual amount of ' M ' is more than that.

Surely you can handle it from here, even with half of your brain
tied behind your back.

Take a good hard look at ' A ', and then go lie down.