Answer:

Step-by-step explanation:
A circle centered at (0,0) with radius r is 
Since your circle has diameter of 12, then its radius is 6. Then 
So a possible answer is: 
If you want to move the location of the center, but keep it on the x-axis, then add or subtract a number to the x, such as this:

The center of this circle would be (-4, 0) which is still on the x-axis.
He can ride his bike 105 km. 30/2 is 15. 15*7 is 105.
:D
Answer:
Can you re-type the question. This doesn't make any sense.
Step-by-step explanation: