Question : Huffman encoding and entropy notes - can someone please explain this note screenshot

Huffman encoding and entropy notes - can someone please explain this note screenshot
This is the results of the a huffman encode.
Code 2 are codes for each letter. code 1 as far as I see are the complements in order to show that they are unique ("no codeword is the prefix of any other code word"). Is this to show that they are unique in the direction showen how is this done and no in the reverse direction? How is this done?
Also how is the entropy, H, calculated at the bottom...
Thanks a million if you can help me :)

Answer : Huffman encoding and entropy notes - can someone please explain this note screenshot

entropy is
-( 0.3*lg(0.3) + 0.25*lg(0.25) + 0.2*lg(0.2) + 0.17*lg(0.17) + 0.05*lg(0.05) + 0.02*lg(0.02) + 0.01*lg(0.01) )
= 2.315
average length =
0.3*2 + 0.25*2 + 0.2*2 + 0.17*3 + 0.05*4 + 0.02*5 + 0.01*5 = 2.35
efficiency = 2.13/2.35