Find the equation of an ellipse with the center at the origin, major axis on the y-axis, and passing through the points (3,2) and (1,6).

a) (x²/4) + (y²/9) = 1
b) (x²/9) + (y²/4) = 1
c) (x²/16) + (y²/81) = 1
d) (x²/81) + (y²/16) = 1