If the Fed supply 20 billion dollars into the commercial banking system, how much more money the commercial banks create and supply?

Depends on the reserve ratio, which in turn determines the money multiplier.

Explanation:

The money multiplier formula = 1 / reserve ratio

For example, if the reserve ratio is 10%, the money multiplier will be 10. If the reserve ratio is 20%, the money multiplier will be 5.

To calculate the total effect of a $20 billion inflow, you must multiply that amount by the money multiplier:

E. g. $20 billion x 10 = $200 billion, or $20 billion x 5 = $100 billion