If the length of a uniform pipe is 45 pounds, then the 18 pound piece is 18/45 the length of the pipe. If 18/45 of the length of the pipe is equal to 3 feet, then we can set up the equation:
(18/45)x = 3ft
Where x is the total length of the pipe. Solving for x:
(18/45)x = 3ft
18x = 135
x = 7.5 feet
We now know that the total length of the pipe before being cut is 7.5 feet. Since the first piece was 3 feet, we know that the second piece must be 4.5 feet (7.5 - 3).
Answer: 4.5 feet