
Why?
We have the isosceles right triangle. The length of legs are 6. Use the Pythagorean theorem:

In general, the formula for calculating the hypotenuse in an isosceles right triangle is 
a - a leg, h - a hypotenuse
Answer:
If a figure has four sides, then it is a kites.
Step-by-step explanation:
When the slope is zero, the line is horizontal. Its equation will be of the form
... y = constant
The y-value of your point is specified as -9, so the equation of the line through that point is
... y = -9