For any triangle T in the xy–coordinate plan, the center of T is defined to be the point whose x–coordinate is the average (arithmetic mean) of the x–coordinates of the vertices of T and whose y–coordinate is the average of the y–coordinates of the vertices of T. If a certain triangle has vertices at the points (0,0) and (9,0) and center at the point (4,3), what are the coordinates of the remaining vertex? Select the correct option:
A) (3,4)	B) (3,6)	C) (4,9)	D) (3,9)	E) (9,6)
Let (a,b) be the remaining vertex.   x: 0 + 9 + a = 3*4. Then a = 3.   y: 0 + 0 + b = 3*3.= 
<gadget id="calculator">3*3.</gadget>
<output>9</output>
9.   The answer is (3,9).
<result>D</result>
For any triangle T in the xy–coordinate plan, the center of T is defined to be the point whose x–coordinate is the average (arithmetic mean) of the x–coordinates of the vertices of T and whose y–coordinate is the average of the y–coordinates of the vertices of T. If a certain triangle has vertices at the points (0,0) and (9,0) and center at the point (4,3), what are the coordinates of the remaining vertex?