Explanation:
she can therefore only spend $10 of the $20.
$8.64 are adjust gone for the card game.
that leaves us with
10 - 8.64 = $1.36
to spend on lollipops.
1 lollipop costs $0.28
so, she can buy a many lollipops as times 0.28 fits into 1.36 :
1.36 / 0.28 = 4.857142857...
that means she can buy 4 lollipops max.
she would keep some change, but not enough to buy a 5th lollipops, because then she would have to cut into the $10 reserve she needs for lunch.
for 5 lollipops she would need $1.40 (5×0.28).