h= number of hours worked
Total= $160
Service call= $55
Hourly cost= $35
Total bill equals service call plus (hourly cost multiplied by number of hours worked)
$160= $35h + $55
subtract 55 from both sides
105= 35h
divide both sides by 35
3= h
ANSWER: The plumber worked 3 hours.
Hope this helps! :)