Single dog is $20 + (10 minutes * $1 per minute) = $<<20+10*1=30>>30.
Two dogs are 2 * ($20 + (7 minutes * $1 per minute)) = $<<2*(20+7*1)=54>>54
Three dogs are 3 * ($20 + (9 minutes * $1 per minute)) = $<<3*(20+9*1)=87>>87
The total is $30 + $54 + $87 = $<<30+54+87=171>>171.
#### 171