To solve for the rate of the second bus, we start from the equation given:
\[ 3(r + 10) + 3r = 282 \]
where \( r \) is the rate of the second bus in miles per hour.
First, we can simplify the equation:
\[ 3r + 30 + 3r = 282 \]
Combine like terms:
\[ 6r + 30 = 282 \]
Now, we can isolate \( 6r \) by subtracting 30 from both sides:
\[ 6r = 282 - 30 \]
\[ 6r = 252 \]
Next, divide both sides by 6:
\[ r = \frac{252}{6} \]
\[ r = 42 \]
Thus, the rate of the second bus is \( r = 42 \) mph.
The correct answer is:
A. R = 42 mph