Question 962413
Let A(3,1,2) and B(5,5,2)

and C is the point on Y-axis its co-ordinates  will be (0,y,0)

if A and B are equidistant from C then 

AC^2=BC^2

therefore, 3^2 + (y-1)^2 + 2^2 = 5^2 + (y-5)^2 + 2^2


solving the above equation gives, y=5