1. **State the problem:** We have an equilateral triangle with each side measuring 9.4 cm, correct to the nearest millimetre (0.1 cm). We need to find the upper bound of the perimeter of this triangle. 2. **Understand the measurement precision:** Since the side length is given as 9.4 cm to the nearest 0.1 cm, the actual length could be as much as 9.45 cm (upper bound) and as little as 9.35 cm (lower bound). 3. **Calculate the upper bound of one side:** $$\text{Upper bound of one side} = 9.4 + 0.05 = 9.45 \text{ cm}$$ 4. **Calculate the upper bound of the perimeter:** Since the triangle is equilateral, perimeter $P = 3 \times \text{side length}$. $$P_{upper} = 3 \times 9.45 = 28.35 \text{ cm}$$ 5. **Final answer:** The upper bound of the perimeter is **28.35 cm**.