Problem help

[moorhouse987]

I'm a new member so forgive me if this is the wrong place to post. I'm a chem eng undergrad and have this issue;

I have this x-y diagram for a distillation column and it basically asks: 'The steps between stages 5 and 6 exactly meets the q line. This means: -
(a) the liquid feed is supplied to stage 6
(b) that the liquid feed is supplied to stage 5
(c) that the diagram would be the same whichever plate was used.

Also it asks if the overall column effeciency is 50%, what is the tray number of the feed F1 if optimally positioned?

Many thanks