In a hypertonic solution the mass of the cell would

The answer would be decrease.

Hypetonic solution means they have a lower water potential than the other side, which is the cell cytoplasm in this case. When the water potential of a side is higher, water molecules would flow from the region of higher water potential to the region of lower water potential. And here, the cell membrane acts as the semi permeable membrane, which is necessary for this movement.

This movement is called osmosis. And, because the water molecules flow from the cell cytoplasm to the solution (due to the water flow down the water potential gradient) , the cell would lose water. This results in the decreased mass of the cell.

Sometimes, if the cell is an animal cell, they may shrink because too much water is lost. If it's a plant cell, it won't shrink but the cell cytoplasm may detach from the cell wall, this phenomenon is called plasmolysis.