Suppose a file system is based on the index allocation strategy for managing blocks. Assume each file has a directory entry giving the filename, first index block, and the length of the file. The first index block points, in turn, to 249 file block and to the next index block. If the file is currently positioned at logical block 2010 and the next operation is to access logical block 308, how many physical blocks must be read from the disk? Explain your answer.