Trying to present an answer assuming slight change in the given reaction to keep consistency with the unit of equilibrium constant.
The reaction and ICE table
Where x mole is the amount of A to be mixed with 4 moles of B initially
The volume of the reaction mixture given is
So at equilibrium the concentration of the components will be
Now equilibrium constant
Inserting the value of
So the amount of A to be added to 4 moles of B is 26 moles