Industry output and market share

Here is a problem that I am trying to figure out:

Wkly. output    Apple Airlines(A)    Big Bird(B)       Chancy Airlines, ltd.(C)
1                     $40                       $20                   $50
2                       30                        25                     40
3                       25                        30                     45
4                       35                        35                     55
5                       50                        40                     65
6                       60                        50                     75

The current fare market price of $45 can't be raised. Thus P=MR=$45

I have to
a) calculate current industry output and the market share of each airline and
b) calculate industry output if the introducation of a high speed passenger train forces airline industry prices down to $35.

I don't know where to begin, can somone please explain this to me?

Thanks