You can put this solution on YOUR website! I think I solved this one earlier this evening. Can you use a graphing calculator? Graph y1 = lnx - 4ln3, and y2 = ln(5/x) on the same grid, and find the point where the graphs intersect.
With the graphing calculator I get approximately x =20.124612, which rounds off to x=20.1246. I think I solved the other problem using logarithms.