15. Mohamed is selling tickets for his home movies. Tickets for friends are $3.00 and
everyone else must pay $5.00 per ticket. If he sold
72 tickets and made $258 how many of each type
did he sell?

The change in y (y being the height of the plant) over 4 weeks was 6 2/3 in.

The average rate of change of the plant's height is therefore

6 2/3 inches

= 1 2/3 inches/week on average.

    4 weeks

The average rate of change of the plant growth per week was 1 2/3 inches.  That would be the decrease per week.