A circle with its center on the line $y = 3x$ in the $1$^st quadrant is tangent to the $y$-axis. .

1. If the radius is $2$, what is the equation of the circle?

   Hint (a):

   What point on the line $y = 3x$ is $2$ units from the $y$-axis?

   Answer (a):

   Use the coordinates of the center and the radius to write an equation in general form.

2. If the radius is $3$, what is the equation of the circle?

   Hint (b):

   See part (a).