There's an important property concerning the sides of a triangle. The length of the longest side must be smaller than the sum of the length of the other two sides. With this in mind let's see each of these four cases one by one.
1) First we have the lengths 12, 12 and 6. Since the two longest sides have the same length we have that the biggest length is 12 and the sum of the other two is 12+6=18. Since 18>12 then these 3 can be side lengths of a triangle.
2) Here we have 17.5, 24.1 and 7.4. The greatest value is 24.1 whereas the sum of the other two lengths is 17.5+7.4=24.9. Since 24.9>24.1 then these 3 can be side lengths of a triangle.
3) Here we have the lengths 4, 11 and 14. The greatest is 14 whereas the sum of the others is 4+11=15. We have that 15>14 then these 3 can be side lengths of a triangle.
4) Finally we have 11, 1 and 6. The greatest is 11 and 1+6=7. This time the sum of the 2 shorter sides is smaller than the length of the longest side so these 3 can not be side lengths of a triangle.
In summary, the first 3 cases can be side lengths of a triangle but the fourth can't.