First, we need to convert feet to miles and seconds to hours.
1 mile is equal to 5280 feet.
So, 1716 feet is equal to (1716/5280) miles or 0.325 miles.
1 hour is equal to 3600 seconds.
So, 3 seconds is equal to (3/3600) hours or 0.00083333 hours.
Now we can calculate the speed of the plane in miles per hour by using the formula:
Speed (in miles per hour) = Distance (in miles) / Time (in hours)
Speed = 0.325 miles / 0.00083333 hours
Speed = 390 miles per hour (rounded to the nearest whole number)
Therefore, the speed of the plane is 390 miles per hour.