Calculate the number 840

Bill and Bob, two Government mechanical engineers, were standing at the base of a flagpole, looking up.
A woman walked by and asked what they were doing.
'We're supposed to find the height of the flagpole', said Bob, 'But we don't have a ladder.'
The woman said, 'Hand me that wrench out of your toolbox.'
She loosened a few bolts, then laid the pole down.
She then took a tape measure from their toolbox, took a measurement and announced, 'Eighteen feet, six inches' and walked away.
Ray shook his head and laughed.
'Ain't that just like a 'Miss-know-it-all' woman?' he said.
'We need the height and she gave us the length!'
Bob and Ray are still working for the Government.