Given the information on the problem, we have that Miss Glover ate 4 slices from the 6 of the cake, then she ate 4/6 of the cake.
Then, Ms. Heinen ate 3/6 of her cake.
Adding these two fractions we get the following:

therefore, Miss Glover and Ms Heinen ate 1 1/6 of cake, or which is the same, one cake and one slice