a. What is meant by the delta of a stock option?

b. You are holding call options on a stock. The stocks beta is 0.75, and you are concerned that the stock market is about to fall. The stock is currently selling for $5 and you hold 1 million options on the stock (i.e you hold 10,000 contracts for 100 shares each). The option delta is 0.8. How much of the market index portfolio must you buy or sell to hedge your market exposure?