In its first month of operations, Skysong, Inc. made three purchases of merchandise in the following sequence: $(1)220$ units at $\backslash (\backslash$$ $10\backslash ),(2)440$ units at $\backslash (\backslash$$ $11\backslash ),$ and $(3)420$ units at $\backslash (\backslash$$ $12\backslash ).$ Assuming there are $140$ units on hand, compute the cost of the ending inventory under the $($a$)$ FIFO method and $($b$)$ LIFO method. Skysong uses a periodic inventory system.