title: TypeError: can only concatenate tuple (not "float") to tuple, problem with density formula
body: <p>I am pretty new with Python and I am given a task to create a model in Python. 
  I have a problem with this formula: 
  <code>density = p/(0.1921 * (T+273.1))</code>.
  It keeps saying: <code>TypeError: can only concatenate tuple (not "float") to tuple</code>.</p>
  
  <p>Does anyone know the solution?</p>
  
  <pre><code>p = 0.699 * exp**(-0.00009 * h) 
  T = -23,4 - 0.00222 * h
  rho = p/(0.1921 * (T+273.1))
  </code></pre>