To find: The speed of car to completely pass the truck.
The speed of car to completely pass the truck is 80.66 mi/h.
Given:
The length of car is 14 ft and the length of truck is 30 ft.
The speed of truck is 5 mi/h and time taken by car to pass the truck is 6 s.
Formula used:
Distance formula is,
Calculation:
Let the speed of car be x ft/s.
Speed of truck in ft/s,
Tabulate the given information into the language of algebra.
In words  In algebra 
Speed of car  x 
Effective speed 

Total distance 

Model the equation for the above information.
Simplify the above equation for x,
Thus, the speed of car to completely pass the truck is 80.66 mi/h.