Answer:
(a) After 8 minutes, the water level of the trough was 28 cm
⇒ rate = 28/8 cm per minute ( = 7/2 = 3.5 cm per minute)
(b) 7/2 cm per minute
For every minute that passes, the level of the water trough increases by 3.5 cm
(c) 28/8 = 21/6 = 7/2
the unit rate is constant, so the water level (y) varies directly with the time elapsed (x)