Teradyne assembles a large printed circuit board called a "backplane." This product is used for communication and storage devices. A few years ago, the company's production rate was $300$ backplanes in seven days in three shifts $(24$ hours a day$).$ Then, Teradyne converted its production process from batch into assembly line. The result was assembling $500$ backplanes in five days in two shifts $(16$ hours a day$).$ Assuming that the same number of workers worked during each shift before and after the conversion, what was the percentage growth in labour productivity?

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