I don't understand how to do this problem 3x + y =9

(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

How many lines can be drawn through points j and k? 0 1 2 3

It says factor each expression completely 8y+48