Answer:
1. No: 16 + 21 = 37 < 39
2. Yes: 34 + 27 = 61 > 58
3. No: 12 + 12 = 24 < 25
Explanation:
Triangle Inequality Theorem
The sum of the lengths of any two sides of a triangle is greater than the length of the third side.
To determine if the given side lengths could form a triangle, sum the two shortest sides and observe if the sum is greater than the length of the longest side.
Question 1

As 37 < 39, the sum of the shortest two sides is less than the length of the longest side, and so the given side lengths cannot form a triangle.
Question 3

As 61 > 58, the sum of the shortest two sides is greater than the length of the longest side, the given side lengths can form a triangle.
Question 5

As 24 < 25, as the sum of the shortest two sides is less than the length of the longest side, the given side lengths cannot form a triangle.