Let us assume then that the center is the origin. If the major axis is 18, then a = 9 and a^2=81. If the minor axis is 16, then b = 8 and b^2=64. Now you can write the equation. Remember that this ellipse is vertical and so a^2 goes under y^2
When you add up all the marbled you get 19 marbles and since their are 6 pink marbles you get 6/19. Since 6/19 is already in simplest form then that is your answer.