Answer
3.5 hours.
Explanation
The first step is to calculate the constant of proportionality.
t ∝ 1/n
t = k/n Where t = time, K= constant and n = number of people
t = k/n
k =tn
= 5×7 = 35
The equation becomes;
t = 35/n
for n = 10,
t = 35/10
t = 3.5 hours.