We can solve the equation \(3(r + 10) + 3r = 282\) step by step.
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Distribute \(3\) to both terms inside the parentheses: \[ 3r + 30 + 3r = 282 \]
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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 \( \boxed{42} \) miles per hour.
To verify, we can calculate the rate of the first bus, which is \( r + 10 = 42 + 10 = 52\) miles per hour.
In 3 hours, the distances traveled by both buses will be:
- Distance by the second bus: \(3r = 3 \times 42 = 126\) miles
- Distance by the first bus: \(3(r + 10) = 3 \times 52 = 156\) miles
Adding the two distances together: \[ 126 + 156 = 282 \text{ miles} \]
This confirms that the calculations are correct. The rate of the second bus is indeed \( \boxed{42} \) miles per hour.