Working alone at its own constant rate, a machine seals \(k\) cartons in \(8\) hours, and working alone at its own const

Working alone at its own constant rate, a machine seals \(k\) cartons in \(8\) hours, and working alone at its own constant rate, a second machine seals \(k\) cartons in \(4\) hours. If the two machines, each working at its own constant rate and for the same period of time, together sealed a certain number of cartons, what percent of the cartons were sealed by the machine working at the faster rate?

A. \(25\%\)

B. \(33\frac13\%\)

C. \(50\%\)

D. \(66\frac23\%\)

E. \(75\%\)

Answer: D

Source: GMAT Prep