7 NAND gates.
Expression after minimization
=B'C' + A'C' + A'B'
= B'C' + A'(C' + B')
=B'C' + A'(BC)'
Now, for the SOP expression, 3 NAND gates.
Additionally, 1 NAND to realise (BC)'
1 NAND to realise to C'
1 NAND to realise to B'
1 NAND to realise to A'