The graph shows what happened to potato cylinders in salt solutions of different strength…

Step 1. Gain. In the solutions with less than about $0.5\ \text{g}$ of salt in 100 mL, where the line is above zero.

Step 2. The same concentration. Where the line crosses zero, at about $0.51\ \text{g}$ in 100 mL.

Step 3. At 0.8 g. The graph reads about $-7.5\%$: the potato lost water.