What is the marble's range if it is fired horizontally from 1.6 m above the ground?

The answer is 6.40 meters.

Explanation:

The speed v = √ (2gh)

v = √ (2*9.8*6.4) = 11.2 m/s

After, finding the time it takes to hit the ground from a height of 1.6 meters.

time = √ (2H:g)

time = √ (2*1.6:9.8)

time = 0.5714 seconds.

Horizontal distance is speed * time = 11.2 * 0.5714 = 6.40 meters.