Three identical units of merchandise were purchased during May, as follows: Magnesium XP Units Cost May 3 Purchase 1 $130 10 Purchase 1 136 19 Purchase 1 142 Total 3 $408 Assume that two units are sold on May 23 for $313 total. Determine the gross profit for May and ending inventory on May 31 using (a) FIFO, (b) LIFO, and (c) average cost methods.