Conjugations of verbs for the formal "you" in Spanish are the same as for the subjects el and ella; in present tense, they usually end in -a.
The option you have checked is in past tense ("I bought this"); the present tense conjugation is compra.
Usted compra esto.
Again, the conjugation of verbs for the formal "you" in present tense almost always end in the letter "a"; the correct conjugation is estudia.
Usted estudia <span>matemáticas.</span>
Answer: She had visited 6 stores
Explanation: She had visited the supermarket, Butcher shop, Stationery, cake shop, shoe store and clothing store.
D. fueron
You would use the past tense verb. In this case it is 'fueron', which translates to 'were'.
Hope this helps. Good luck! :)