Answer:
43 km/h
Step-by-step explanation:
If the car is going past you at 50 km/h, then all the objects inside appear to be going 50 km/h. The fly is flying 7km/h in the opposite direction, and would appear to be going 7 km/h slower. Therefore, as 50 - 7 is 43, the fly would appear to be going 43 km/h. Hope this helps :D