Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
It takes 10 minutes to wash a car, 15 minutes to change oil, and 30 minutes to change a set of tires.  If mike washes 9 cars, changes the oil on 6 cars, and changes two sets of tires how many hours did he work?

### Response:
He spent 10 minutes *9 cars = <<10*9=90>>90 minutes washing cars
He spent another 15 minutes * 6 cars = <<15*6=90>>90 minutes changing oil.
He spent 2 cars * 30 minutes = <<2*30=60>>60 minutes changing tires.
He spent 90 + 90 + 60 = <<90+90+60=240>>240 minutes working
He spent 240 / 60 = <<240/60=4>>4 hours working
#### 4