Hi sud21,
While most Test Takers would approach this question with Algebra, it can actually be solved rather easily by TESTing VALUES.
We're never given any limitations on how much total money is actually spent, so the individual values (and the total) can be ANYTHING, as long as the values relate to one another as described. So, working through the information that is provided....
IF....
Brian = $1,000
Mike spent $400 more than Brian....
Mike = $1,400
John spent $1,200 less than Charles (we'll come back to this in a moment)
Charles spent $400 more than Mike...
Charles = $1,800
Now, back to the prior info - John spent $1,200 less than Charles...
John = $600
The question asks how many MORE dollars Brian spent than John:
Brian = $1,000
John = $600
$1,000 - $600 = $400
Final Answer: A
GMAT assassins aren't born, they're made,
Rich