The height of the chalkboard is 3ft. Since the chalkboard has a perimeter of 18ft, that means that the 2 lengths of the board are 6 ft or 12 ft added together. Afterwards, subtract 12 from 18 ft ( 18 - 12), which shall get you 6ft. Then, divide 6 by 2, since there are two sides that represent the height.
Therefore, the height is 3 ft.
