Distance of Falling Object

The distance traveled by a falling object **(subject only to gravity, with wind resistance ignored)** is directly proportional to the square of the time it takes to fall that far. If an object falls 100 feet in 2.5 seconds, how far does it fall in 5 seconds?

MY WORK:

I developed the equation d = k/(t^2) from the given information, where d = distance, k is the constant of variation and t = time in seconds.

After doing the math, I got d = 25 feet, which makes no sense. The right answer is 400 feet. How do I get 400 feet? Is my equation wrong?