I have two fraction homework questions i need help on..I am totally stuck. Please help me if you know how to solve it. Thank you, your help is greatly appreciated!!

1.) A water is purification plant works by passing the dirty water through three filters in turn. The first takes out all but 1/4 of the dirt in the water, the second leaves 1/5 of the dirt reaching it and the last takes out 2/3 of what's left.

(a) What fraction of the dirt is left in the water after it has gone through the plant?

(b) What fraction of the dirt has the plant removed?

2) A large pizza costs $12.75, three friends decide to split one. Jack takes a third, and then Jill takes a third of the remainder and then Tom takes half of what's left.

(a) How should they split the total cost so that each pays an amount proportional to what he has eaten so far?

(b) Can they split the remaining pizza so that everyone ends up having eaten the same total amount? If so, how?

PLEASE HELP ME!!...It would AT least help if someone taught me how to start it, or teach me how to do it step by step, so i tackle similar problems on my test ><..Thank you