A rectangular tank is 100cm, 30cm wide and 12cm deep. The volume of liquid it will hold is?

Assuming that you mean 100cm in length, I think I know the answer, but message me if I'm wrong so that I can correct myself!

Volume is L • W • H where L is length, W is width, and H is height.

To find the volume you have to multiply all the dimensions, so 100 * 30 * 12 = 36,000, and since its 3 dimensional we use cm^3 which is centimetres cubed.