I have addresses 158.37.20.0 to 158.37.23.254 available and is supposed to divide them among 4 LAN's with the lowest possible number of addresses allocated to each lan.

Any then a short list of the unallocated ranges.

LAN 1: 150 clients
LAN 2: 170 clients
LAN 3:  90 clients
LAN 4:  50 clients

          Network address    Netmask         Num.addr   From          To             Broadcast
LAN 1     158.37.20.0/24     255.255.255.0     254      158.37.20.1   158.37.20.254  158.37.20.255
LAN 2     158.37.21.0/24     255.255.255.0     254      158.37.21.1   158.37.21.254  158.37.21.255
LAN 3     158.37.22.0/25     255.255.255.128   126      158.37.22.1   158.37.22.126  158.37.22.127
LAN 4     158.37.23.0/26     255.255.255.192    62      158.37.23.1   158.37.23.62   158.37.23.63

Free      158.37.22.128/25   255.255.255.128   126    158.37.22.128   158.37.22.254  158.37.22.255
Free      158.37.23.64/26    255.255.255.192    62    158.37.23.65    158.37.23.126  158.37.23.127
Free      158.37.23.128/25   255.255.255.128   126    158.37.23.128   158.37.23.254  158.37.23.255