This riddle might look like you have to crunch numbers in order to solve it, but it doesn't involve any math at all.
The Guardian pointed out the simple solution: turn the picture upside down and you'll see that the numbers are in numerical order from 86 to 91. Therefore, the car's parking spot number is 87.
You can read the full explanation here.
This, Ladies and gentleman, this is the reason why smart people can pretend to be stupid, but stupid people can never successfully pretend to be smart.
PS: the person that made the image did not understood the riddle.