Okay I'm having trouble with rate of change here is the problem " At 4:00 AM, there were 700,000 gallons of water remaining in a reservoir. After 4 hours of irrigation, there were 200,000 gallons of water remaining. Write an equation that describes the number of gallons of water as a function of the time the field had been irrigated. " so which would it be
a) y = -125,000x + 700,000
B) y = -200,000x + 700,000
c) y = 700,000x
d) y = -700,000x - 200,000
please explain

Question

Okay I'm having trouble with rate of change here is the problem " 	At 4:00 AM, there were 700,000 gallons of water remaining in a reservoir. After 4 hours of irrigation, there were 200,000 gallons of water remaining. Write an equation that describes the number of gallons of water as a function of the time the field had been irrigated. " so which would it be 
a)	y = -125,000x + 700,000
B) y = -200,000x + 700,000
c)	y = 700,000x
d)	y = -700,000x - 200,000
please explain