R3#sh run | b ip dhcp
ip dhcp excluded-address 180.40.7.129
ip dhcp excluded-address 180.40.7.131 180.40.7.134
!
ip dhcp pool Prob15
   network 180.40.7.128 255.255.255.224
   default-router 180.40.7.132
   dns-server 208.28.1.82
   domain-name MyCCIE
   option 150 ip 20.20.20.20
!
ip dhcp pool R4Pool
   host 180.40.7.130 255.255.255.224
   client-identifier 0063.6973.636f.2d30.3033.302e.3835.6633.2e37.3034.302d.4661.302f.30
!



to have R3 serve an address to R3:

R7#sh run int fa 0/1
Building configuration...

Current configuration : 254 bytes
!
interface FastEthernet0/1
 ip address 180.40.7.131 255.255.255.224
 ip helper-address 180.40.7.66

end