In a B+ tree, the requirement of at least half-full (50%) node occupancy is relaxed for which one of the following cases?

Consider two files systems A and B, that use contiguous allocation and linked allocation, respectively. A file of size 100 blocks is already stored in A and also in B. Now, consider inserting a new block in the middle of the file (between 50^th and 51^st block), whose data is already available in the memory. Assume that there are enough free blocks at the end of the file and that the file control blocks are already in memory. Let the number of disk accesses required to insert a block in the midele of the file in A and B are n_A and n_B, respectively, then the value of n_A + n_B is _____________.