Steps to solve:
x^3 - 125 = 0
~Add 125 to both sides
x^3 = 125
~Take cube root of both sides
x = 5
Best of Luck!
A is not a line of symmetry
The triangle must be isosceles, due to the perpendicular bisector. Therefore, the expression 20 - 15 can be used to yield an answer of B. 5.
Hope this helps!