A rock is submerged in a rectangular prism whose base measures 9cm by 15 cm. If the water level rises from a height of 8cm to 12cm. What is the volume of the rock?

What I did:
V= area of base× height of prism L×W×h
9cm×15cm= 135
8cm×12cm= 96
(I'm not sure what I am supposed to do now. I know you have to subracat the volume of rectabgular prism by the water level rising, but I'm confused on how to do it)

1 answer

Most direct way:
The volume of the rock equals the change in the volume of the tank.
The change in the height was 4 cm.
So the volume of the rock is (9)(15)(4) cm^3
= 540 cm^3

or, along your thinking

volume of tank at the start
= (9)(15)(8) or 1080 cm^3
volume after rock is inserted
= (9)(15)(12) or 1620 cm^3
change in volume caused by the rock
= 1620 cm^3 - 1080 cm^3
= 540 cm^3 , as above