Statistic help? Exam in 3 hours.

In country A 30% of people who drink tea have sugar in it. In country B 65% of people who drink
tea have sugar in it. There are 3 million people in country A who drink tea and 12 million people in
country B who drink tea. A person is chosen at random from these 15 million people.

i. Find the probability that the person chosen is from country A.
ii. Find the probability that the person chosen does not have sugar in their tea.
iii. Given that the person chosen does not have sugar in their tea, find the probability that the person
is from country B.

I know everything apart from probability questions. Could you tell me exactly how you arrived to the answer?
(optional: could you tell me points to remember during probability questions?)

Yo, dawg, i hear wat ur saying, stats can b a serius b*tch, like did u no blacks are 6 times mor likely 2 go 2 jail dan wites? dats sum f*cked up s*it right der. dont worry tho Vanilla gud wif numbas, so