Machines X and Y produced identical bottles at different constant rates. Machine X, operating alone for 4 hours, filled part of a production lot; then machine Y, operating alone for 3 hours, filled the rest of this lot. How many hours would it have taken machine X operating alone to fill the entire production lot?

(1) Machine X produced 30 bottles per minute.

(2) Machine X produced twice as many bottles in 4 hours as machine Y produced in 3 hours.

From statement (2),

Work done by X in 4 hours = 2W

Work done by Y in 3 hours = W

3W is the size of the entire production.

It took machine X 4 hours to do 2W. It will take 6 hours for X to do 3W.

Therefore, I pick (B).

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