For the second triangle:

Let's analyze the pattern in the given triangles. We need to find a consistent rule that relates the numbers on the sides to the internal number.

• For the second triangle: The numbers on the sides are 3 and 5. The internal number is 15. If we multiply the side numbers: $3 \times 5 = 15$. This matches the internal number.

• For the third triangle: The numbers on the sides are 7 and 3. The internal number is 20. If we multiply the side numbers: $7 \times 3 = 21$. This does not match 20.

Since simple multiplication doesn't work for both, let's look