Regina has 4 pigs/cow * 20 cows = <<4*20=80>>80 pigs.
She could sell the pigs for 80 pigs * $400/pig = $<<80*400=32000>>32000.
For the cows Regina would get 20 cows * $800/cow = $<<20*800=16000>>16000.
In total Regina would earn $16000 + $32000 = $<<16000+32000=48000>>48000.
#### 48000