We are given that an object has an acceleration of 6 m/s^2. According to Newton's second law we have that the force is the product of the mass by the acceleration:

Where:

We can solve for the acceleration by dividing both sides by the mass:

Since the original acceleration is 6 m/s^2 we have:

Now, for the new acceleration, we are given that the new force is 3 times the original force and the mass is double the original mass, therefore, we can substitute:

But, we already established that:

Therefore:

Therefore, solving the operations, the new acceleration is:

Therefore, the acceleration is 9 meters per second squared.