posetcay:
Considering there is no way to kill black in the corner, even with ko, if opponent really wants to live as pointed out by Sadaharu, I changed the solution to capturing outside stones.

Sadaharu:
To add on, after C19 B16 C15, white can play at B18 and still live the corner

posetcay:
SGF

posetcay:
I think the answer doesn't really make sense here. This is a really heavy ko for the attacker and if opponent really wants to live in the corner he can play C1 B4 C5 B2. Thats why the correct answer should be to start with B2 and take the outside in good shape.