Peter has an NQSO through his employer. The strike price is…

Peter has an NQSO through his employer. The strike price is $15, which happens to be the current market price. Peter exercises this option 2 years later when the stock is trading at $45 per share and then sells it 6 months later at $52 after a better than expected earnings report. What is the tax impact at the time that Peter sells his shares? Note that the exercise and sale are in two different years.