Minimum number of 2-input NAND gates required to implement the function, f=($$\overline X $$+$$\overline Y $$)(Z+W) is

For the identity AB+$$\overline A $$ C + BC= AB + $$\overline A $$ C, The dual form is

The Boolean function A+BC is a reduced form of

The minimum number of 2-input NAND gates required to implement the Boolean function Z=A$$\overline {B\,} $$C, assuming that A, B and C are available, is