Respuesta :

nilbert
The rate of change represents the depth of liquid every three square feet sprayed.

For every square foot of land, the depth decreases by 0.8 of an inch.

Hope this helps!
mathmate
It was answered in the last question:

Rate of change = (21.4-19)/(0-3)=2.4/(-3) = -0.8 in of liquid / sq. ft

He's right.  The previous answer was backwards.  Now corrected.