<human>:  Greg has his own dog walking business. He charges $20 per dog plus $1 per minute per dog for walking the dog. If he walks one dog for 10 minutes, two dogs for 7 minutes and three dogs for 9 minutes, how much money, in dollars, does he earn?
<bot>: How much does Greg charge for one dog? ** Single dog is $20 + (10 minutes * $1 per minute) = $<<20+10*1=30>>30.
How much does Greg charge for two dogs? ** Two dogs are 2 * ($20 + (7 minutes * $1 per minute)) = $<<2*(20+7*1)=54>>54
How much does Greg charge for three dogs? ** Three dogs are 3 * ($20 + (9 minutes * $1 per minute)) = $<<3*(20+9*1)=87>>87
How much money does Greg earn? ** The total is $30 + $54 + $87 = $<<30+54+87=171>>171.
#### 171