What is the first term of the sequence defined by an = 3(n-3) ? My teacher said it was 0, I just don't understand the work behind it.

Acertain volume of water contains 100000 hydrogen atoms and 50,000 oxygen atoms how many hydrogen atoms are in a volume of water containing 4 million oxygen atoms

Travis and paula went to lunch.travis ordered a sandwich for $7.50 and paula ordered a burger for $5.25.after lunch,they left a 15% tip for the waiter.how many money did they spend altogether?

Type the next three numbers in a sequence 80, 90, 85, 95, 90, 100, 95, 105