Help, I am not sure how to find the percent of increase in a problem or even the percent of decrease. My parents have no idea either!!!

Examples: The sales of HiTop sneakers rose from $4billion to $4.4 billion. What is the percent of increase?

One week, a certain stock market index went down from 1,863 to 1,677. What was the percent of decrease?

Find the percent of chan $20,200 to $17,350.