PLZ HELP NO LINKS 20 POINTS

(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

Which of the fallowing best completes the sequence 5,10,15, a) 30 b) 22 c)25 d)35

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much