There are 50 total patrons. 16 like lattes, 12 like espressos, and 8 like both drinks.
Add the two totals for patrons that like either lattes or espressos:

8 patrons like both drinks, so subtract this from the amount of patrons that like either drink:

20 patrons like at least one drink.
Subtract the amount of patrons that like a drink from the total amount of patrons:

30 patrons like neither drink.