Working alone at its own constant rate, a machine seals k cartons in 8 hours

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?

25%
33 1/3%
50%
66 2/3%
75%

Machine A---- 1hr---K/8 carton
Machine B-----1 hr--K/4

Together In 1 hr k/4+k/8 = 3k/8 cartons

% = k/4/3k/8 = 8/12 *100 = 200/3=66.67%(Ans)(D)