Conditional proabability from a tree diagram.

I am stuck on question number (3) below:

¾ of the population in Siniestra is left-handed and ¼ are right-handed. In an examination, it was shown that 80% of the left-handed passed and 90% of the right-handed passed.

1)Complete the tree diagram

2) Find the probability of

i) the people are left handed and they passed

ii) all passed.

3) A person was chosen at random from the population. He had passed the examination. Using the answers you provided in Question number 2. Find the probability that

i) the person chosen from the population is left handed.