Volume · Superchallenge problem

An aquarium is $60$ cm long, $30$ cm wide and $40$ cm tall, and it is $\dfrac{3}{4}$ full of water. Then $30$ identical stones are dropped in and sink to the bottom. The water rises to the very top and $1.5$ liters spill over the edge. One liter is $1000$ cubic cm. What is the volume of one stone, in cubic cm?