Wich three lengths could be the lengths of the sides of a triangle

In order for a triangle to actually be a triangle, the sums of 2 sides has to be greater than the 3rd side.  in the first option, 10+15 > 24, 15+24 > 10, and 10+24 > 15 so this is a triangle.  in the second option, 9+22 > 11, 22+11 > 9, but 9 + 11 is only 21, so this is not a triangle.  option 3: 12+5=17, which, although is not greater than 17 it is the same which would make this an isosceles triangle, which is a triangle, as long as 12+17 > 5 and 5+17 > 12, which of course they are.  in the last option: 7+6 is only 13 which is not greater than 21, so the last one is not an option either.  only the first and the third.