Please help with either or both

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

What is the point-slope equation of a line with slope -5 that contains the point (6,3)

Afarmer has a large field that is x feet in length. he wants to fence in a rectangular section in the middle of the field , leaving a length of 100 feet of open field behind each end of the fenced rectangle.he also wants the width of the fenced-in space to be 100 feet less than its length. find the expressions to represent the length and width of the fenced section of the field