The minimum Tier 1 capital increases from 4% in Basel II to 6%, applicable in 2015, over RWAs. This 6% is composed of 4.5% of CET1, plus an extra 1.5% of Additional Tier 1 (AT1).

So in this case, Tier I capital must be at least $24 million:

$0.06% \times `400` \text{ million} = \`24` \text{ million} $