Aslice of potato is placed in a hypertonic salt water solution. in a few hours, what would be the appearance of the potato slice?

The potato slice would turn soft and may shrink.

This is because osmosis occurred. Hypertonic solution means that the solution has a lower water potential than the other side, which is the potato cell cytoplasm here, through the semi permeable membrane (cell membrane). In osmosis, water molecule will flow from a region of higher water potential to a region of lower water potential, it is a natural movement and doesn't need extra energy input.

Because the potato cell cytoplasm has a higher water potential, the water flows away from it and the cell lose water. When it lose water, the cell membrane may get to a point where it shrinks and detaches from the cell wall, and this phenomenon is called plasmolysis. When the cell cytoplasm shrinks and water flowed away, the potato cell may lose its trugor pressure and become soft and a decrease in size.