Need Help with NBDE Part 2 Qs

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Hi All,

Could you please help me out with the formulas needed to calculate the below questions?.

Q1. Using "B" speed film exposure to the patient at 3 feet is 1 roentgen. What would the exposure be with "D" speed film at 6 feet?(Assume all other exposure factors to be the same)

Q2. At 90 kVp and 15mA at a target film distance of 8 inches, the exposure time for a film is 1/2 second. Under the same situation, the exposure time at 16 inches is....?

Thanks for your help.