Answer:
Cylinder H has the greater volume. 
Explanation:
Recall that the volume of a cylinder is given by: 

Where r is the radius and h is the height. 
Cylinder H has a radius of 4.5 meters and a height of 3 meters. Thus, its volume is: 

Cylinder J has a diameter of 7 meters and a height of 4.5 meters. The radius is half the diameter, so Cylinder J's radius is 3.5 meters. Thus, its volume is: 

Thus, Cylinder H has the greater volume.