The base of triangle is 15 cm and height is 12 cm the height of another triangle of double the area having base 20 cm is :

Answer: Option C

Given base of triangle and its height is 15 cm and 12 cm respectively
Area of first triangle :
$$\begin{array}{rl}& =\frac{1}{2}\times \text{Base}\times \text{Height}\\ & =\frac{1}{2}\times 15\times 12\\ & =90\text{ sq}\text{. cm}\end{array}$$
According to the question,
Let height of triangle be h cm
Area of new triangle = 180 sq. cm
Base = 20 sq. cm
$$\begin{array}{rl}& \Rightarrow 180=\frac{1}{2}\times 20\times \text{Height}\\ & \Rightarrow \text{h}=\frac{2\times 180}{20}\\ & \Rightarrow \text{h}=18\text{ cm}\end{array}$$