Three friends own a landscaping business. the number of hours each person spends on the project

Assuming that the landscaping business is open for 12 hours, opens at 8AM and closes at 8PM. There are three friends, to be fair, they will divide the total number of hours. 12 hours divided by 3 is 4 hours for each friend. Therefore the minimum hours that one friend should spend for the landscaping business is at least 4 hours. 

Maybe the answer is 20mm. all i really did was just multiply, which is obvious.