Let the sides of triangle be a = 18 cm, b = 24 cm and c = 30 cm.
Let s be the semi-perimeter of the triangle.
\(s=\frac{1}{2}(a+b+c)\)
\(s=\frac{1}{2}(18+24+30)\)
\(s=36\,cm\)
The smallest side is 18 cm long. This is the base.
The height corresponding to the smallest side is 24 cm.