Find the area of a triangle if its perimeter is 36 and the radius of the inscribed circle is 3.

It is known from the properties of the inscribed circle that its radius is equal to the ratio of the area of the circumscribed triangle to its half-perimeter. By proportion, we find that the area of a triangle is equal to the product of the radius of the inscribed circle by the half-perimeter of this triangle.
The half-perimeter of a triangle is half of its perimeter, that is, in this problem, the half-perimeter will be 36/2 = 18.
Find the area of the triangle:
S = r * p = 3 * 18 = 54
Answer: 54