$1.$ Call options on a stock are available with strike prices of $$18,$ $$20,$ and $$22,$ and expiration dates in $3$ months. Their prices are $$3,$ $$2,$ and $$1\mathrm{.}5,$ respectively. Explain how the options can be used to create a butterfly spread and a reverse butterfly spread. Construct a table showing how profit varies with stock price for the reverse butterfly spread.