Answer:
$40
Explanation:
Brian starts at $100, then loses 1/4th of the money,
100/4 = 25,
then you subtract 25 from 100, which gives you 75
With the remaining $75, he spends $15 on girl scout cookies,
75 - 15 = 60
He then has $60 remaining, but while walking home, loses 1/3 of the total amount.
60/3 = 20,
you then subtract 20 from 60, which gives you 40
Therefore, $40 is what is remaining.