Yang is employed by a CCPC. In 2014, he was granted stock options to purchase 500 of his employer's shares for $10 per share. The shares were valued at $12 per share on the day he received the stock option. In 2016, when the shares were valued at $18 per share, he exercised the option and bought all 500 shares. He sold the shares in 2021 at the market price of $25 per share. 

Required:

a) Calculate the impact as a result of the stock option on Yang's net income for tax purposes for each of 2014, 2016, and 2021. Explain the impact to net income for tax purposes for each year. 

b) If Yang's employer were a public company rather than a CCPC, calculate the impact on Yang's net income tax purposes for each of 2014, 2016, and 2021. Explain the impact to net income for tax purposes for each year.