1) Read the problem properly (I misread 256 KB to be 256 Bytes)
2) 256KB = 256 * 1024 Bytes
3) How many numbers can be used in 256KB of data (and how much space is used storing them)

mean 256*1024 = total bytes.
(total bytes)/8byt . as for 18 dijit no in c double is used which is of 8 byte so it is 32768 = size of aray (double)