I seem to have trouble deciding whether or not to use 'a' or 'an' when followed by quantities:
Built (a/an) 120 lb. robot.
Built (a/an) 18"x 18"x 18" robot.
In terms of pronunciation, the first case could go like:
Built a one-hundred-and-twenty pound robot.
Built an a-hundred-and-twenty pound robot.
Which would it be?