Help me with this real answers only

Which equations represents circles that have a diameter of 12 units and a center that lies on the y-axis? check all that apply

When keisha installed a fence along the 200 foot perimeter of her rectangular back yard, she left an opening for a gate. in the diagram below, she used x to represent the length in feet of the gate? what is the value? a. 10 b. 20 c. 25 d. 30

Pls the last one and it has to be like number 6