The midline of an isosceles triangle, parallel to the side, is 4 cm, and the base is 5 cm.

The midline of an isosceles triangle, parallel to the side, is 4 cm, and the base is 5 cm. Find the perimeter of the triangle.

Either with the condition that something is wrong, or with the answer.
The middle line, which is given according to the condition of the problem, is two times smaller than the lateral side (property of the middle line). We get that the lateral side is 8 cm. In an isosceles triangle, there are two such equal lateral sides. The basis is given by condition, we find the perimeter:
P = 8 + 8 + 5 = 21 (cm).
Answer: the perimeter of the triangle is 21 cm.