Answer: C
lets assume order of b+ tree is n.
B+ tree internal node has n-1 keys and n node (child) pointer.
Given : key size: 14 bytes
Child pointer : 6 bytes
we have ,
block size = (n-1) * key size + n * child pointer
512>=(n-1)*14+n*6
512>=14n-14+6n
n=(512+14)/20
n=526/20
n=26.3
n=26