37.5 inches
If the model is an accurate scale model, then the ratio of a dimension in the model to the dimension in real life will remain a constant. So we have
6/75 = 3/X
where
6 = length of model
75 = length of actual car
3 = width of model
X = width of actual car
Solving for x, gives
6/75 = 3/X
6 = 225/X
6X = 225
X = 37.5
So the actual car width is 37.5 inches.
