20 16: 20 (1-6%)+X car ownership.

20 17:[20( 1-6%)+X]( 1-6%)+X = 20( 1-6%)？ +( 1-6%)x+x

20 18:20( 1-6%)? +( 1-6%)? x+( 1-6%)x+x

……

20( 1-6%)^n+[ 1-( 1-6%)^n]x/6% & lt； 40

When n tends to infinity, (1-6%) n tends to 0.

Therefore, x