On October 30th, low tide occurred at 1:00 pm PST.  High tide will occur at midnight.  The freighter Yakisoba Maru sits unloaded at Dock 50.  Her ladder's rungs are numbered from 1 at the top to 40 at the bottom.  Each rung is spaced 18 inches apart.  The tide will rise at a rate of one-half foot per hour.  At 1:00 pm, the water level is exactly at Rung #20.  What rung will be closest to the surface of the water at high tide?