density =mass/volume
The volume of the rock is= volume of raised after rock was put in the cylinder which is calculated by finding the difference in volumes
That is 36.2 -25=11.2mls
convert ml to CM^3
1ml=1cm^3 what about 11.2ml=11.2cm^3
Density is therefore= 15g/11.2 cm^3= 1.34 g/cm^3