18. The traffic inspector noticed that out of 20 cars that passed on the road to the airport, 14 were "Ladas," 15 were dark-colored, 17 were driven by men, and in 18 cars, there were passengers besides the driver. For what minimum number of cars could all 4 of these characteristics be true?
18. Out of the total number of cars, 6 did not have the first feature (not "Zhiguli"), 5 did not have the second, 3 did not have the third, and 2 did not have the fourth. Therefore, the maximum number of cars that do not have at least one feature is 16 $(6+5+3+2=16)$. The remaining $4(20-16=4)$ have all four features.