Answer:
221 mm
Explanation:
The dimension 74 mm is presumed to mean that the actual length could be anywhere in the interval [73.5, 74.5). So, the minimum perimeter is ...
3 × 73.5 = 220.5 ≈ 221 . . . millimeters
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The perimeter of an equilateral triangle is 3 times the side length, since all three sides of the triangle are the same length.