Answer: Hannah's dad is providing POSITIVE reinforcement.
Explanation: Positive reinforcement can be defined as the act of giving encouragement to a person who exhibits a particular behaviour with the result that such behaviour is repeated.
Positive reinforcement strengthens a behavior or certain response.
From the question, Hannah's dad provided positive reinforcement by treating her to a chocolate sundae each time she brings home a straight A report card. This is done solely to motivate Hannah and to increase chances of getting good grades.