uTypeError: unsupported operand type(s) for -: 'str' and 'str'
<p>I get this error:</p>

<blockquote>
  <p>uTypeError: unsupported operand type(s) for -: 'str' and 'str'</p>
</blockquote>

<p>From this code:</p>

<pre><code>print "what is your name?"  
x=raw_input()
print "Are you woman or man?"
y=raw_input()
print "how old are you?"
z=raw_input()
print "at what age did you or will you first travel in an plane?"
f=raw_input()

print "This is a story about a ",y," named ",x
print z-f ,"years ago",x, " first took an airplane."
print " the end"
</code></pre>

<p>Why?</p>
