To find the rate of change in the plane's altitude, we need to calculate how much the altitude decreases per minute.
The pilot descends 4,000 feet in 3.5 minutes. To find the rate of descent in units of feet per minute, we can use the formula:
\[ \text{Rate of descent} = \frac{\text{Total change in altitude}}{\text{Total time}} = \frac{4000 \text{ feet}}{3.5 \text{ minutes}}. \]
Now, performing the calculation:
\[ \frac{4000}{3.5} \approx 1142.8571 \text{ feet per minute}. \]
Rounding this to the nearest hundredth, we get:
\[ \text{Rate of descent} \approx 1142.86 \text{ feet per minute}. \]
So, the rate of change in the plane's altitude is approximately 1142.86 feet per minute, and since the plane is descending, we can state that it is 1142.86 feet per minute down.