So what we want to know is how long is the car that is 6% shorter then the other car. We can look at it this way: the shorter car is 94% the lenght of the longer car. Lets call the length of the shorter car x, then we have the equation: 94% * 3.9m=x. Or, (94/100)*3.9=x. Now we solve for x and get: x= 3.666m. So the shorter car is 3.666 m long.