I want to fast for 30days. Only eat fruit once a day to keep me alive..
but uhm...how much weight would I lose?
Would it be all muscle or fat?

you would loose about 25 pounds, not advised, becasue they second you take a step outside your house you will most likely faint.....it will also all be muscle and fat

You'd probably lose the muscle first.
Which is honestly, pretty bad.
You should be losing the fat, not the muscle.
Starvation = NOT a good way to lose weight.

dont do it
its not healthy
my science teacher told me that when you fast for a long time that your stomach starts to feed off ur fat and it could cause stuff like blackouts headspins and u could be sent to hospital if it gets bad
if you seriously want to loose alot of weight then go to a gym(get on an electric bike 4 about 40 min and put it on hard- dont stop peddling) and do not eat after 7:00 pm and dont eat take away
if you do this you will loose at least 3 kg a week and thats alot
it worked 4 me and im sure it will work 4 you

why the rush.
first of all that is the worst thing you could ever do to your body
and second as soon as you go back to eating you will gain it all back and more trust me.
you will lose both because as you starve your body it will begin eating itself
and when your body realizes its not getting food it will begin to store anything it gets instead of digesting it properly so that fruit won't go through it will just be saved in your body