Answer:
Symmetry about y-axis
Explanation:
If f(x) is a even function and (6,8) is one the points on the graph of f(x).
Even Function: It makes symmetry about y-axis. The value of y is same from origin to left side and right side of y-axis. 
Even function: 

For even function, if (6,8) point on f(x) then (-6,8) must be on f(x). 

The value of y=8 is same 6 unit from left and right of y-axis 6. 
Both points are on function because it is symmetry about y-axis for even function.