please solve with working much appreciated

Answer:
5 cm
Step-by-step explanation:
What you have there is an equilateral triangle. An equilateral triangle is a triangle that has sides with equal lengths and interior angles are equal as well. So if all angles are equal in a triangle, then that means that this is an equilateral triangle. So we can say that if one side of this triangle is 5cm
then the n would also be equal to 5cm.