Answer:
See below.
Step-by-step explanation:
She is wrong because 3 times the perimeter of one triangle is the sum of 9 sides of the triangles.
In the shape we see that some of the sides of the triangles are 'shared' and dare not part of the perimeter of the shape, - the perimeter is only the length of 5 sides of a triangle.
So the perimeter is less than the sum of the sides of the 3 triangles.
