multiply 80 * 24, to get the total amount sold each day. divide by 10 to get the amount per hour.
positive slope > increasing line
negative slope > decreasing line
slope of the line tell us the steepness of the line and the sign of the slope tells us whether the line is increasing or decreasing
when the sign of the slope is positive then the line is increasing
when the sign of the slope is negative then the line is decreasing