I respond to myself.
Of corse the answer is
x = [1, 3, 5, 7, 9]
y = x.find {|v| v*v > 30 }  #and now I have the variable
puts y => 7
 Sorry, I am a very beginer and I was iduced in error because in the 
book the ex was [1, 3, 5, 7, 9].find {|v| v*v > 30 } and it didn't came 
to me to write puts before such a expresion, and I worked on v.
Thanks again
Adrian

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