To treat his 20 dogs, Mr. Sean charged Khalil 20*$60 = $<<20*60=1200>>1200
Khalil also paid $40*60 = $<<40*60=2400>>2400 to Mr. Sean to treat his cats.
Altogether, Khalil paid Mr. Sean $2400+$1200 = $<<2400+1200=3600>>3600 to treat his pets.
#### 3600