Your aircrafts total seating capacity is 240 pax.
Your doors allow 375 to safely exit.
Your rafts only fit 330 so this becomes the max allowable config.
Now Door 1L is out of action. You instantly lose 110 from that door pair.
330-110 = 220.
As your max pax load is 240 but you now only have raft space for 220 you must block out 20 seats.
Note - Don't confuse raft space with door capacity. Doesn't matter which doors they leave by they'll swim to the nearest raft (in theory).