To solve this logical reasoning problem, we need to analyze the Venn Diagram and identify the region that represents individuals with only long and black hair. Let's break down the diagram:

• The triangle represents individuals with long hair.
• The rectangle represents individuals with short hair.
• The square represents individuals with black hair.
• The circle represents individuals with grey hair.

We are interested in finding the number that represents individuals with only long and black hair. This means we need to find the intersection of the triangle and the square that does not overlap with the rectangle or the circle.

By examining the diagram, we observe:

• Number 12 lies within both the triangle and the square, meaning these individuals have long and black hair.
• Number 12 is outside the rectangle and the circle, ensuring that these individuals do not have short or grey hair.

Thus, the number that represents only long and black hair is 12.