If you consider what the slope looks like for a vertical line, it is an infinite slope. What that means is that you cannot have a y-value in your equation:
x = 3
This x-value would be a vertical line that passes through all y-values for x = 3. So you can replace them in (3, y) with any value, and it will be included in the linear equation x = 3.
Since we know that the radius of circle p is 7 times that of the radius of circle o we can say that radius of circle p equals 7x and the radius of circle o is x. using the area formula we can say that area of circle p equals