Question

which sentence is more formal? updating the downtown promenade will cost twenty million dollars but will certainly attract more tourists. updating the downtown promenade will attract more tourists but will cost the city twenty million bucks.

Explanation:

Formal language avoids colloquial terms. The second sentence uses "bucks" (colloquial for money), while the first uses "twenty million dollars" (formal) and "certainly" (proper adverb) without slang. So the first sentence is more formal.

Answer:

Updating the downtown promenade will cost twenty million dollars but will certainly attract more tourists.