In the past four months, not including today, Erica has 80 kg * $20/kg = $<<80*20=1600>>1600 worth of fish.
Today, Erica trawled 80 * 2 = <<80*2=160>>160 kg of fish.
Thus today's earnings are 160 kg * $20/kg = $<<160*20=3200>>3200.
Her total earnings are $3200 + $1600 = $<<3200+1600=4800>>4800
#### 4800