Agarage chaged mr tilton $48 in parts and $36/h in labor many hours did the garage spend on mr tilton's carr if total bill was$156

156 = 36x + 48

108 = 36x

3 = x

They spent 3 hours on the car. 

48 is a constant, so we take this out first
156 - 48 = 108

Since 36 is the variable, we can divide the above result to get the amount of hours.
108/36 = 3 hours