Plz help asap i beg u

What is the y intercept of f(x)=(1/2)^x?

The product of 3 and a number increased by 8 is 31

Jody bought 20 shares of amazon at the close price of $121.00. she bought 20 more shares a year later at the price of $127.00. two years later, she sold all of her shares at the price of $133.00. her broker charges $50 for each transaction. after all of these transactions, how much money did jody make?