Answer: Ben has $112.
Explanation: There are context clues given in the question that points to the answer. The first clue is that Ali has $40 more than Ben; the second clue is that Deming has 3x what Ben does - see the below for how I arrived at the answer.
$600 - $40 = $560
$560 / 5 = $112 [dividing by 5 because Ben and Ali have the same (minus the $40) and Deming has 3 times what Ben does - that means all together, there is 5 equal amounts of money split between them without the $40]