Answer:
Very sorry if this is wrong but, I think the answer would be 48 inches.
Explanation:
If every 3ft. = 2in. then I believe you would first divide the length and width by 3. So 6 divided by 3 is 2 and 18 divided by 3 is 6. Then you would multiply 2 and 6 by 2 since every 3ft = 2in.