ANSWER and EXPLANATION
We want to identify the reason why some objects fall faster than others.
The reason for this is that the air provides significantly more resistance to the feather's downward motion than the brick does. The air acts as a frictional upward force pushing against gravity and delaying the rate at which the feather falls.
The brick, however, can cut through the air as if it were not there at all. Due to air resistance, items that are more dense, i.e. have more mass, fall at a faster rate than objects that are less dense.
That is the answer.