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Yes 100 Steem Power is equal to 100 Steem. Powering down means converting it back into Steem over 104 weeks. A little gets converted each week. Steem Power grows by itself every minute or so..protecting you against most of the inflation. Steem is transferable to exchanges so is much more liquid.

Can i sell this account? What is this account value?

Your account value is $450 and since all of that is Steem Power it will take you 2 full years to cash out. I cant imagine you'd be able to sell the account. I don't know a safe way to do that or even if it would be ok to do.

I can find a intermediary. Very thank you. Can we be friend :) ?

Sure. Good luck to you!