Help i need to finish it today And can you explain the steps so i wont need help next time or if you don’t want to its okay :)

(note i put the graph in so plz )the graph shows the amount of water that remains in a barrel after it begins to leak. the variable x represents the number of days that have passed since the barrel was filled, and y represents the number of gallons of water that remain in the barrel. what is the slope of the line

When the ball has traveled a distance of

Ill mark the brainliest if you me with the these three questions 7,8,9