Answer:
See below in bold.
Step-by-step explanation:
The triangular piece of cloth is a right triangle because 41^2 = 40^2 + 9^2 (By the Pythagoras theorem).
So the area of one piece = 1/2 * 9 * 40 cm^2.
The total amount of cloth required for one umbrella = 10 * 1/2 * 9 * 40
= 1800 cm^2.
The total cost = 1800 * 0.25 = Rs 450.