A equilateral triangle isn’t 6n-15. What’s the expression that represents the length of each side

Question

A  equilateral triangle is 6n-15. What’s the expression that represents the length of each side. 

Answer 1

I assume that you mean "the perimeter of an equilateral triangle is 6n-15".  In an equilateral triangle, all three sides have the same length.  If s = the length of a side, then the perimeter is s+s+s = 3s:

 

3s = 6n-15

 

Solve for s.