Query to get Requisition Approval Amount

We need to build a customer report to get the Requisition Amount and Approval Amount.

select 

prha.requisition_number

,sum(prla.amount) "Requistion Amount"

,NULL "Approval Amount"

from

from por_requisition_headers_all prha

,por_requisition_lines_all prla

where 1=1

AND prha.requisition_header_id = prla.requisition_header_id

GROUP BY

prha.requisition_number

We're not able to find the column/table to get requisition approval amount.

How we can get the requisition approval amount ?

Thanks