For leaf nodes order is-
n*(K+RP)+BP <= Block size
and for non-leaf nodes order is-
n*BP+(n-1)K <= Block size
Here question is about Leaf nodes so it would be
n*(K+RP)+BP <= Block size
Therefore, n*(9+7)+6 <= 1024
16n<=1018
n <= 63.6
So, n is 63. Hence option A is correct.