Mark partially drained his pool to clean it. At 1:00 P.M., he started to refill it. At 5:00 P.M., the pool had 10,400 gallons of water. At 9:00 P.M., the pool had 13,800 gallons of water. If filling the pool is modeled by a linear function, how many gallons of water still remained in the pool when he first started to refill it?
If this is a linear function, then difference would be equal for each instances.
We know, there are 4 hours between 1.00 PM & 5.00 PM and also 5.00 PM to 9.00 PM
So, Difference between 9.00 to 5.00 = 13,800 - 10,400 = 3400
Now, at 1.00 PM it would be: 10,400 - 3,400 = 7000
In short, Your Answer would be 7,000 Gallons
Hope this helps!