For k>0, let Rk denote the region bounded by the graph of y=x+1k, the x–axis, and the vertical lines x=0 and x=2. When Rk is revolved about the y–axis, the resulting solid has volume 12π. Determine the value of k.
(a) 2−ln36
(b) 2+ln36
(c) 2−ln312
(d) 6(2−ln3)