The sides of a triangle are 6 cm, 7 cm and 8 cm.Find the sides of a similar triangle, the perimeter of which is 84 cm

Let’s find the perimeter of this triangle:
P = 6 + 7 + 8 = 21 (cm).
Now let’s calculate how the perimeter of such a triangle relates to the perimeter of this one:
84: 21 = 4.
Since the triangles are similar, the ratio of the sides of a similar triangle to the sides of this triangle will be equal to 4. Therefore, such a triangle will have sides:
6 x 4 = 24 (cm),
7 x 4 = 28 (cm),
8 x 4 = 32 (cm).
Answer: 24, 28 and 32 cm.