Answer:
Yes, 10.5 cm, 8.0 cm and 4.0 cm can be the side lengths of a triangle.
Step-by-step explanation:
We have been given three lengths as 10.5 cm, 8.0 cm and 4.0 cm. We are asked to determine whether these side can be the side lengths of a triangle.
We will use triangle inequality theorem to solve our given problem.
Triangle inequality theorem states that sum of two sides of a triangle must be greater than 3rd side. Using triangle inequality theorem we will get 3 inequalities as:

True

True

True
Since all the three side lengths satisfy triangle inequality theorem, therefore, 10.5 cm, 8.0 cm and 4.0 cm can be the side lengths of a triangle.