How to filter for distinct values and apply multiple filters in QGIS attribute table?

I am very new to QGIS. I am doing an assignment for class where we have to answer several questions about data obtained from Global Fishing Watch. One of the questions is how many vessels have a tonnage greater than 1200? I know how to filter for this. However, the data includes multiple voyages for each ship. As you can see in the attached screenshot, when I filter for tonnage, many of the ships appear more than once (the MMSI field is the ID number of the ships). My question is how do I filter for tonnage AND make it so that each ship will only appear once? I figure I need to filter by tonnage and filter the MMSI for distinct values, but I am unsure how to apply two filters to a search and I need to know how I can filter a field so that it will remove duplicates. I have a feeling that the "count_distinct" function is what I need, but so far it hasn’t worked, I think my syntax is incorrect. As for applying two filters, just putting "and" between my expressions has not worked thus far. As I said I just started and do not yet have a hang of how the expression syntax works.