The acceleration of the bike is equal to
opposing the movement (to the right).
Why?
Since after the rider slams the brakes, the bike came to a stop, we know that the acceleration is opposite to the velocity/movement.
We can use the following equation to calculate the acceleration:

So, substituting, we have: (let's consider negative to the left and positive to the right)

The negative sign means that the acceleration's direction is opposite to the movement.
Hence, we have that the acceleration is equal to
opposing the movement (to the right).
Have a nice day!