Angles that create a triangle always add up to 180.
To find sides that create triangles, we have to use the Triangle Inequality Theorem.
It's where side A + B will always be greater than side C
and B + C will always be greater than side A
and A + C will always be greater than side B.
So let's check all of these answers and pick the one that's incorrect.
A.
10 + 25 + 145 = 180?
Correct!
B.
9 + 15 > 9?
Correct!
15 + 9 > 9?
Correct!
9 + 9 > 15?
Correct!
C.
40 + 70 + 60 = 180?
Incorrect! 40 + 70 + 60 = 175 which is less than 180.
The answer is three angles measuring 40 m, 70 m, and 60 m.