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 <em>almost </em>exactly what the problem <em>does</em> 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 <u>least</u> it could be. The actual amount of ' M ' is <u>more</u> 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.