Find the local time of Yanga in Tanzania, which is located at longitude 39° East, if it is 12:00 noon at Kinshasa in the Democratic Republic of Congo (DRC), located at longitude 14° East.

Both locations are in East longitude, so we subtract their longitudes.

$$\text{Longitude difference} = 39^\circ \text{ E} - 14^\circ \text{ E} = 25^\circ$$

We know that the Earth rotates $15^\circ$ in 1 hour, or $1^\circ$ in 4 minutes.

$$\text{Time difference in minutes} = 25^\circ \times \frac{4 \text{ minutes}}{1^\circ} = 100 \text{ minutes}$$

Convert 100 minutes into hours and minutes:

$$100 \text{ minutes} = 1 \text{ hour and } 40 \text{ minutes}$$

Since Yanga ($39^\circ$ E) is to the East of Kinshasa ($14^\circ$ E), Yanga's time will be ahead of Kinshasa's time.
Kinshasa's time is 12:00 noon.

$$\text{Yanga's time} = 12:00 \text{ noon} + 1 \text{ hour and } 40 \text{ minutes}$$ $$\text{Yanga's time} = 13:40$$

The local time of Yanga is 1:40 PM.

$\text{1:40 PM}$