Please reason step by step, and put your final answer within \boxed{}.
In the ancient Chinese mathematical masterpiece "The Compendious Book on Calculation by Completion and Balancing," there is a problem as follows: "Listening over the wall, one hears the guests dividing the silver, not knowing the number of people or the amount of silver. If each person receives 7 taels, there will be 4 taels left over; if each person receives 9 taels, there will be 8 taels short. The question is: how many guests are there? How much silver is there?" This means that there are a certain number of guests dividing a certain amount of silver. If each person receives 7 taels, there will be 4 taels left over; if each person receives 9 taels, there will be 8 taels short (in the question, catty and tael are old units, with 1 catty = 16 taels). The question is: how many guests are there? How much silver is there? Let the number of guests be $x$ and the amount of silver be $y$. According to the question, the system of equations can be written as ____.
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