The answer is 13.
Because this is a kite, the diagonals intersect perpendicularly or with a 90° angle.
In the triangle DIC, which is a right triangle, the legs are 5 and 12. To find the hypotenuse, we use Pythogarean theorem:

Plug in the givens:

Take the squares:

Take the square root of both sides:

We find the line segment DC. In the question it says "BD = DC". So BD is equal to 13.
Answer:
15
Step-by-step explanation:
f(x) = 3x -12 for x = 9
f(9) = 3(9) -12
27-12
15