Answer:
1.76 g/mL
Explanation:
You need to find the volume. You can do this by subtracting the volume of the water and the rock by the volume of the water.
72.7 mL - 50 mL = 22.7 mL
Now that you have volume, divide the mass by the volume to find the density.
39.943 g/22.7 mL = 1.76 g/mL