Final answer:
The statement is true; increasing the diameter of a pipe from 4 to 6 inches increases capacity by 2.25 times if the velocity remains the same.
Step-by-step explanation:
The question relates to the fluid dynamics principle that the carrying capacity of a pipe is related to its cross-sectional area. According to the data provided in the question, increasing the diameter of a pipe from 4 inches to 6 inches increases the capacity by a factor of 2.25. Given that the velocity remains constant, the capacity of the pipe is proportional to its cross-sectional area, which is dependent on the square of the diameter. Since the area increases by a factor larger than the increase in diameter, the new 6-inch pipe will indeed be able to carry 2.25 times as much material as the 4-inch pipe, if the velocity remains unchanged.