Hi Angeles L
The slope intercept form can be used to represent your situation
y = mx + b
y = f(x) = mx + b
m = rate of loss 16 for 16 gallons per minute, it is a loss so the sign will be negative
Equation is f(x)= -16x + 500
f(15) = -16(15) + 500 = 260
When f(x) = 0 then x is 500/16
x intercept is 31.25 minutes
The function represents a continuous loss of water from a full tank (500 gals=full tank) at a rate of 16 gallons per minute. When x is zero this represents when the tank was full before the horse kicked a hole in it. When f(x) is zero this gives the time it took to empty the 500 gallon tank.
I hope this helps