Review the excerpt from Tennyson's "Lady of Shalott, then answer the question.

Willows whiten, aspens quiver,
Little breezes dusk and shiver
Thro' the wave that runs forever
By the island in the river
Flowing down to Camelot.
Four gray walls and four gray towers,
Overlook apspace of flowers,
And the silent isle embowers,
The Lady of Shalott.

How many feet are in Line 9?