For each $20 rebate offered to a buyer, the number of sets sold will increase by 200 per week: The slope is (-20/200)
Formula of the slope:

For the given situation:

Use the equation above to solve p(x) in terms of x:

Then, the function representing the demand p(x) is:

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b) The largest value x can be is the value when p(x)=0:
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