You pay $2.40 for 3434 pound of grapes. your friend buys a pound of grapes at the same time and estimates that he will pay $1.80. what can you say about your friend's estimate?

If your friend was working from your figures, then his estimate was
wy off, like in outer space.

If you paid $2.40 for 3434 pounds, then that works out to something
like 0.007¢ for each pound.  His estimate of $1.80 is more than 2,500
times as much as you paid for each pound. 

Even allowing some slack for the quantity discount that you surely
must have been awarded for buying 1.7 tons of them all at once, still
that doesn't support his wild estimate in any way. 

He'd be better off buying a few pounds from you, at, say, 50¢ a pound. 
He needzum, you gottum, he'll gettum, and you'll  never missum.  That way,
you'll both make a killing, and it's a win-win-win all around.

3cm and 6 and 9 cm that a possibility of that question