To represent this situation algebraically, we can use the formula:
y = mx + b
where y represents the water level in inches, x represents the time in minutes, m represents the rate of change (decrease) in inches per minute, and b represents the initial water level in inches.
We know that the initial water level is 15 inches, and it is decreasing at a rate of 0.5 inches every minute. Therefore, we can write the equation as:
y = -0.5x + 15
where y is the water level in inches and x is the time in minutes.
To find how long it will take for the water level to measure 9 inches deep, we can substitute y = 9 into the equation and solve for x:
9 = -0.5x + 15
Subtracting 15 from both sides, we get:
-6 = -0.5x
Dividing both sides by -0.5, we get:
x = 12
Therefore, it will take 12 minutes for the water level to measure 9 inches deep.