Mark M. answered 04/06/19
Mathematics Teacher - NCLB Highly Qualified
Equilateral triangle:
Draw and label a diagram
The height is s√3/2. It is also the apothem!
This by 30-60-90 triangle
64 = (s/2)(s√3/2)(1/2)
128 = (s/2)(s√3/2)
512 = s2√3
295.60 ≈ s2
17.193 ≈ s