To determine the rate of the second bus (r), we'll solve the equation you've provided:
\[ 3(r + 10) + 3r = 282 \]
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Distribute the 3: \[ 3r + 30 + 3r = 282 \]
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Combine like terms: \[ 6r + 30 = 282 \]
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Subtract 30 from both sides: \[ 6r = 252 \]
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Divide both sides by 6: \[ r = 42 \]
Thus, the rate of the second bus is \( r = 42 \) mph.
So the correct response is: r = 42 mph.