Answer: 2 hours
Explanation
The equation for this problem is 78 + 45x = 168
1) First subtract 78 from both sides
78 +45x = 168
-78 -78
___________
45x = 90
2) Now divide 45 from 45x to leave the x by itself and do the same for the other side
x = 2
It took 2 hours to repair the car