Triangle Perimeter from Side Lengths — Direct Sum: Find the perimeter of a triangle with sides 6 cm, 4 cm, and 5 cm.

Introduction / Context:
Perimeter is the simplest aggregate measure of a polygon—just the sum of side lengths. This item checks careful reading and arithmetic rather than geometric reasoning. Even so, confirming triangle validity is good practice to avoid degenerate cases.

Given Data / Assumptions:

• Sides: 6 cm, 4 cm, 5 cm
• Units are all in centimetres
• Triangle inequality holds (6 < 4 + 5, etc.)

Concept / Approach:
No formulas beyond addition are required. Perimeter P equals the sum of the three sides in consistent units. Because the values are small integers, the result should be an integer in centimetres with no need for rounding.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 14 cm and 16 cm are off by −1 and +1 due to common mental-sum slips.
• 18 cm and 20 cm ignore one side or add extra length.

Common Pitfalls:

• Mistyping integer sums; always re-check totals when only simple arithmetic is involved.

Final Answer:
15 cm.