He cuts down 2*20=<<2*20=40>>40 trees by himself
Each of his brothers cuts down 20*.2=<<20*.2=4>>4 fewer trees per day
So they each cut down 20-4=<<20-4=16>>16 trees
So for the next 3 days they cut down 20+16*2=<<20+16*2=52>>52 trees per day
So they cut down 40+52*3=<<40+52*3=196>>196 trees
#### 196