Answer:
see explaination
Step-by-step explanation:
If I am to select I will select the strategy Impute the missing values . Because rather than deleting and all the other strategies. This is the best option because, this is an optional field as described there is no need for such accurate information about salary.
If we want to maintain this field we can just fill the value by identifying the similar records which is the other customers who is visiting the same no of times and fill that.