Final answer:
In a triangle with the total of their interior angles summing up to 720 degrees, the type of triangle is obtuse-angled (option B).
Step-by-step explanation:
The sum of the interior angles of a triangle is a constant value of 180 degrees. If the total of the interior angles in a triangle is 720 degrees, it suggests that this triangle has more than three sides, indicating a polygon with more than three vertices. In this case, the triangle must be a quadrilateral (option B).
A quadrilateral can be seen as two triangles sharing a common side. If the interior angles of one triangle exceed 180 degrees, it means that the triangle is obtuse-angled, and the sum of the interior angles of the quadrilateral will be greater than 360 degrees.
In contrast, acute-angled triangles have interior angles totaling less than 180 degrees, right-angled triangles have a total of 180 degrees, and scalene refers to a triangle with all sides and angles of different lengths and measures.
Therefore, the correct answer is that the triangle, in this case, is an obtuse-angled triangle due to the excess of 180 degrees in the sum of its interior angles.