3. A journey is divided into three segments: uphill, flat, and downhill, with the length ratios of these segments being $1: 2: 3$. The time ratios spent on each segment by a person are $4: 5: 6$. It is known that the person's speed uphill is 3 kilometers per hour, and the total length of the journey is 50 kilometers. How long did it take this person to complete the entire journey?
3. $10 \frac{5}{12}$
3.【Solution】The length of the uphill road: $50 \times \frac{1}{1+2+3}=\frac{25}{3}$ (km),
The length of the flat road: $50 \times \frac{2}{1+2+3}=\frac{50}{3}$ (km),

The length of the downhill road: $50 \times \frac{3}{1+2+3}=\frac{75}{3}$ (km),

The time taken for the uphill road: $\frac{25}{3} \div 3=\frac{25}{9}$ (hours),

The total time taken to complete the journey: $\frac{25}{9} \div \frac{4}{4+5+6}=\frac{25}{9} \times \frac{15}{4}=10 \frac{5}{12}$ (hours).