X can do a certain work in 40 hours. Y is 25% more efficient than X, and Z is 28% more efficient than Y. Working together, X, Y and Z will complete the same work in:
\(\tfrac{800}{77}\,\text{hours}\)
\(\tfrac{160}{9}\,\text{hours}\)
\(\tfrac{400}{11}\,\text{hours}\)
\(\tfrac{200}{13}\,\text{hours}\)