If the triangles are similar, this means that the ratio of their corresponding sides are equal and that the ratio of their areas is equal to the square of the ratio of these sides. To answer the question above,
area of rst / area of xyz = (3 inches / 2 inches)²
27 / x = (3/2)²
The value of x is equal to 12. Thus, the area of triangle xyz is 12 square inches.