A square pyramid has a height of 18cm and base that measures 12cm on each side explain whether tripling the height would triple the volume of the pyramid?

Yes, the volume triples. When you have a height of 18, the volume will equal 864. (Volume of a pyramid is the area of the base x the height x 1/3)
18*3=54. When you plug this in to the above listed formula, the volume will be 2592. Divide that by three and you get 864.