Answer: 7cm
Step-by-step explanation:
The perimeter of a triangle is calculated by adding the length of the 3 sides together. Let the third side be x , then
x + 9 + 6 = 22
x + 15 = 22
Subtract 15 from both sides , that is
x = 22 - 15
x = 7
Therefore : the third side is 7cm