Create a function that takes an old price old, a new price new, and returns what percent the price decreased or increased. Round the percentage to the nearest whole percent.
percentage_changed("$800", "$600") ➞ "25% decrease"
percentage_changed("$1000", "$840") ➞ "16% decrease"
percentage_changed("$100", "$950") ➞ "850% increase"
N/A