Hello Abdullah,
From the shared screenshot I comprehend that the displacements of the floor and driver are available, and that their respective accelerations are to be calculated.
Similar to the use of the “Derivative” block to calculate floor velocity, in your screenshot (indicated below), another "Derivative” block can be connected to the floor velocity to obtain the floor acceleration. 
A similar process can be followed to obtain the driver acceleration. The final model would look similar to the image below. 
Note that the sudden onset of the input signal at the start of the simulation causes an initial spike in the velocity and acceleration. To address this issue, you can refer to the following MATLAB Answers link.
Hope this helps!
