how distribute aligned memory wholly controlling customary library?

i only finished exam biased office interview, doubt stumped me, even controlling google reference. i'd organization it:

the memset_16aligned duty requires 16-byte aligned pointer upheld it, crash.

a) distribute 1024 bytes memory, align 16 byte boundary?

b) giveaway memory after memset_16aligned executed.

{    
   vacant *mem;
   vacant *ptr;

   // answer a) here

   memset_16aligned(ptr, 0, 1024);

   // answer b) here    
}