SQL & PL/SQL

I have this query:

SELECT INL.INV_ID,CS.CUST_ID ,CS.CUST_ACTIVE_DEFECTING,INL.ITM_QTY

FROM MGC.INVOICE_LINES INL, MGC.INVOICES INV, MGC.CUSTOMERS CS

WHERE INL.INV_ID = INV.INV_ID

AND INV.BILL_CUST_ID = CS.CUST_ID

AND CS.CUST_ACTIVE_DEFECTING = 'Y'

;

I want to find info between 30 and 60 days. I am trying to figure out using SYSdate - INV.INV_CLOSE_DATE in the query and get the results between 30 and 60 days.

Thanks,

Tom