this is a badly-worded question due to the usage of the phrase “at first”.
if taken to mean the amount of money he had at the beginning of the question,
it would lead to an unreasonable answer of $33.33~.
if you take it to mean the amount of money he had at the beginning of the
2nd day, you’ll get $40 for the answer.
$40 – $4 = $36 (4/36 -> 1/9)
1/4 of 36 = $9
9-4 = $5 (difference between the 2 day’s expenditure)
in any case, you should clarify the question with the setter.