How much mass of water gets out?

Question: A cylindrical cocktail glass 15cm high and 35cm^2 in cross section contains water up to the 10cm mark. A card is placed over the top and held there while the glass is inverted. When the support for the card is removed, what mass of water must leave the glass in order that rest of the water will remain in the glass, if one neglects the weight of the card?

My work:

Here, the value of h is coming zero which is not possible because if height is zero then mass will also be zero.

Please tell me what’s the mistake here?