Donaldsons pay $15/hour = 15*7 = $<<15*7=105>>105.
The Mercks pay $18/hour = 18*6 = $<<18*6=108>>108.
The Hilles pay $20/hour = 20*3 = <<20*3=60>>60.
The total amount Layla earned is 105 + 108 + 60 = <<105+108+60=273>>273.
Layla earned $273 for babysitting.
#### 273