The solution that the app builder should use to meet DreamHouse Realty's needs is Master-Detail Child Object. A master-detail relationship can be used to create a parent-child relationship between two objects, where the child records inherit the sharing and security settings of their parent record. The app builder can create a roll-up summary field on the parent object to calculate the highest value of all child records. Option B is incorrect because Text Area (Long) is a field type that allows users to enter up to 131,072 characters on one line, which is not suitable for this requirement. Option C is incorrect because Multi-select Picklist is a field type that allows users to select multiple values from a predefined list, which is not suitable for this requirement. Option D is incorrect because Lookup Object is not a valid term, but rather Lookup Relationship, which is a type of relationship that links two objects together, but does not support roll-up summary fields.