Given three level page table,
2 || 9 || 9 || 12 ||
PTE size = 4B
Page Table Size = No.of entries in page in page table * entry size
PTS of 1st level page table = $2^{2}* 4B = 16B$
PTS of 2nd level page table = $2^{9}* 4B$ and we have $2^{2}$ 2nd level Page tables.
So PTS of 2nd level page table = $2^{9}* 4B * 2^{2} = 8KB$
PTS of 3rd level page table = $2^{9}* 4B $ and we have $2^{2}* 2^{9}$ 3rd level page tables.
So PTS of 2nd level page table = $2^{9}* 4B * 2^{2} * 2^{9} = 2^{20} * 4B = 4MB$
So Total overhead = 16B + 8KB + 4MB $\approx$ 4MB.