Question 193898
The sum of any two sides of a triangle must be larger than the length of the remaining side.

1) 20 + 15 < 40. So the side cannot be 20
2) 30 + 15 > 40
15+40 > 30
40 + 30 > 15
So 30 can be an answer
3) 40 + 40 > 15
15 + 40 > 40
So 40 can be an answer
4) 50+40 > 15
40+15 > 50
50 + 15 > 40
So 50 can be an answer