Answer:
(a) $12.25
Explanation:
You want to know the amount Tom had left after using a $20 bill to purchase milk for $3.50 and cookies for $4.25.
Amount remaining
To find what Tom had left, subtract the cost of the purchases from the original amount.
$20 -3.50 -4.25 = $12.25
Tom has $12.25 left.