Answer:
Let's call the number we're trying to find "x".
According to the problem, when this number is decreased by 40% of itself, we get 54.
In other words,
x - 0.4x = 54
Simplifying the left side, we get:
0.6x = 54
Dividing both sides by 0.6, we get:
x = 90
Therefore, the number we're looking for is 90.