To find the total number of cups of water \( b \) when there are 8 rest stops (\( r = 8 \)), we need to calculate the total cups of water from the rest stops and the finish line.
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Calculate the total cups of water at the rest stops: \[ \text{Cups at rest stops} = 66 \times r = 66 \times 8 = 528 \]
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Add the cups of water at the finish line: \[ \text{Cups at finish line} = 59 \]
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Calculate the total cups of water \( b \): \[ b = \text{Cups at rest stops} + \text{Cups at finish line} = 528 + 59 = 587 \]
Thus, the value of \( b \) when \( r = 8 \) is: \[ \boxed{587} \]