Please,can you help me?

[hmdsaeedy]

I am study in this term Laser Physics course from engineering book
"Laser Electronics" by "Joseph T. Verdeyen"
and I need the solution for this problem in 3rd edition:
problems in chapter 6(Resonant Optical Cavities):20,13,12

 

[antoker]

I think that everyone is capable of reading fonts in normal size ;) Homework questions should be posted in homework section. Before asking for help we'll need you to show, what were your attempts at a solution.