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'Flower Show' printed from https://nrich.maths.org/
Answer: 9 hours.
4 gardeners 4 flower beds
4 hours
4 gardeners 4 flower beds
6 hours ($\times \frac64$)
4 gardeners 4 flower beds
9 hours ($\times \frac64$)
6 gardeners 6 flower beds
9 hours ($\times \frac 64$ for more flower beds
and $\div\frac64$ for more gardeners)