Hi, we are trying to figure out which two cars can't be the same color. Since we know that 1 can't be orange and 4 can't be green, we know that the only way for 1 and 4 to be the same color is for them both to be purple.
However, this is not allowed. There are only two purple cars, and one of them must be in either 5 or 6. So, A is impossible.
