, 2021

Elina and Gustavo start by running and walking for 12 minutes.

Since there are 60 minutes in 1 hour, 12 minutes equals $\frac{1}{5}$ of an hour.

When Elina runs at 12 km/h for $\frac{1}{5}$ of an hour, she runs $\text{12 km/h 1 5 h = 2.4}$ km to the north.

When Gustavo walks at 5 km/h for $\frac{1}{5}$ of an hour, he walks $\text{5 km/h 1 5 h = 1}$ km to the east.

At this point, Elina and Gustavo start to travel directly towards each other.

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As they change direction, we use the Pythagorean Theorem to calculate their distance from each other. Using this, we obtain $\text{(2.4 km ) 2 + (1 km ) 2 = 2.6 km}$.

Since Elina continues to travel at 12 km/h, Gustavo continues to travel at 5 km/h, and they travel directly towards each other, they close the gap at a rate of $\text{12 km/h + 5 km/h = 17 km/h}$.

Thus, it takes $\text{2.6 km 17 km/h 0.153 h}$ for them to meet.

Since there are 60 minutes in an hour, 0.153 h is equivalent to roughly 9.18 minutes.

Since Elina and Gustavo leave at 3:00 p.m. and travel for 12 minutes and then for an additional 9 minutes, they meet again at approximately 3:21 p.m.