Hi,
Create three formulas like this:
For current: (K10<=30)*J10+0
For > 30 days: (K10>30 AND K10<=60)*J10+0
For > 60 days( K10>60 AND K10<=90)*J10 +0
Note:Make use of boolean operators at bex level to write if else conditions.
Check out this sap help document for reference.
http://help.sap.com/saphelp_nw70/helpdata/EN/23/17f13a2f160f28e10000000a114084/content.htm
Hope this helps.
Regards,
AL