Search using 2 dropdown boxes

I’ve searched for a solution extensively and can’t find one. I want to be able to search for posts based on their existence in 2 categories and I want these categories to be displayed in 2 dropdown boxes.

The first drop down box would be location e.g. The child categories of Country (Boston, New York, San Francisco). The second drop down box would be Services e.g.(Apartment, House, Condo). I want people to be able to search Boston for either All Services or just one service i.e. Apartment.

Any help is appreciated. Thanks