Well slope means a surface of which one end or side is at a higher level than another; a rising or falling surface. So pretty much its just saying he had 6 litters used 4 of those litters and had a remainder of 2. So you can say the slope means that he was decreasing in litters by using 2 litters every 1 hour. I don know really if it´s correct so, sooopppeeerrrr sorry. :( :) bye
