input: 
  def linear_regression(X, Y):
      """Performs linear regression on given X and Y values and predicts the value of Y for a new X value.
      
      >>> linear_regression([1,2,3,4,5], [3,5,7,9,13])
      [15.8]
      """
      import numpy as np
      from sklearn.linear_model import LinearRegression
      
      X = np.array(X).reshape(-1,1)
      Y = np.array(Y)
      
      model = LinearRegression()
      model.fit(X, Y)
      
      return model.predict([[7]])
  
output:     import numpy as np
      from sklearn.linear_model import LinearRegression
      
      X = np.array(X).reshape(-1,1)
      Y = np.array(Y)
      
      model = LinearRegression()
      model.fit(X, Y)
      
      return model.predict([[7]])