Th area of a right triangle is A = 1/2 (ab), where a and b are the legs of the right angle. So area of the base is, A = 1/2 (9 x 12) = 108 cm2. With 2 bases, total area of base is 108 times 2, which is equal to 216 cm2. The other side of the triangular base nypotenuse) can be computed by Phythagorean theorem. Hypotenuse = square root of sum of the suare of 9 and 12. This is equal to 15 cm. There are other 3 rectangular faces with the following dimensions: 9 by 10 cm, 12 by 10 cm and 15 by 10 cm. Area of the other faces are 90, 120 and 150 cm2, by multiplying the length and width, only. Total area is 576 cm2.
