If the total production of mangoes was 400, then orange production was 400+200 = <<400+200=600>>600 kg of oranges.
Since apple production was twice the total production of mangoes, Mr. Sergio had 2*400 = <<2*400=800>>800 kg of apples.
The total quantity of fruits produced at Mr. Sergio's farm is 800 kg of apples+600 kg of oranges + 400 kg of mangoes = <<800+600+400=1800>>1800 kg of fruits.
If Mr. Sergio sold the fruits at $50 per kg, his total income from the sales is 1800*$50 = $<<1800*50=90000>>90000.
#### 90000