In a triangle ABC, the middle line of which is 3cm, 6cm, 7cm. Determine the perimeter of ABC.

1. The middle lines MP, MK, KP are parallel to the sides of AC, BC, AB, respectively. MP = 3 centimeters, MK = 6 centimeters, KR = 7 centimeters.

2. The lengths of the sides of the triangle (according to the properties of the middle line) are equal:

AC = 3 x 2 = 6 centimeters. BC = 6 x 2 = 12 centimeters. AB = 7 x 2 = 14 centimeters.

3. The total length of all sides of a given geometric figure (perimeter) is equal to:

6 + 12 + 14 = 32 centimeters.

Answer: the total length of all sides of a given geometric figure (perimeter) is 32 centimeters.