Since a safe following distance to drive is 2 car lengths for every 10mph, you would need to multiply 2 by 6 to get 12 because the car length increase by 2 per 10mph. So increase 10mph 6 times would give you 12 car lengths. Then the remaining 5mph would just mean that you would be 1 car length away because it's half, making you 13 car lengths away at 65mph
