In July 2015, an investor entered a long position in a call option to buy
1,000,000 USD and simultaneously entered a long position in a put option to
sell 1,000,000 USD at a same strike rate of 21,600 VND per USD, same
expiration date. The call option premium is 300 VND per USD and put option
premium is 400 VND per USD. Describe the profits or loss the investor will
make in VND as a function as follows: Y = aX + b.