Now, we calculate total size.
Total page table entries at 3rd level = 8 pages * (26 entries per page) = 512
Total page table entries at 2nd level = 1 page * (28 entries per page) = 256
Total page tabl entries at 1st level = Total page table entries at 2nd level = 256
$\therefore$ Total entries = 512 + 256 + 256 = 1024 entries
Each page table entry occupies 4B
$\therefore$ Total size of page table for the process = Total page table entries * size of Page table entry = 4KB