The equation that relates acceleration, initial velocity, final velocity, and time is:
\[ v = u + at \]
Where:
- \( v \) = final velocity
- \( u \) = initial velocity
- \( a \) = acceleration
- \( t \) = time
Using this equation, we can solve for the acceleration of the car from rest to 30 m/s:
\[ 30 = 0 + a \times 12 \]
\[ a = \frac{30}{12} = 2.5 \, \text{m/s}^2 \]
Now, to find the time it takes for the car to go from rest to 15 m/s with the same acceleration, we can use the same formula:
\[ 15 = 0 + 2.5t \]
Solving for \( t \):
\[ t = \frac{15}{2.5} = 6.0 \, \text{s} \]
So, the time it takes the car to go from rest to 15 m/s with the same acceleration is 6.0 seconds. Therefore, the answer is (C) 6.0s.