If e1 and e2 are the eccentricities of the ellipse, ${{{x^2}} \over {18}} + {{{y^2}} \over 4} = 1$ and the hyperbola, ${{{x^2}} \over 9} - {{{y^2}} \over 4} = 1$ respectively and (e1, e2) is a point on the ellipse, 15x2 + 3y2 = k, then k is equal to :