Answer:
The answer to your question is: t = 4 hours 
Explanation:
Data
Milton v = 8 km/h
time = 4 hours
Harriet v = 16 km/h
Formula
v = d/t or d = vt
Process
Find the distance travel by Milton in 4 hours
 d = (8 )(4) = 32 km
Find the distance travel by each person
Milton d = 32 + 8t
Harriet d = 16t
 Match them 16t = 32 + 8t
Solve for t 16t - 8t = 32
 8t = 32
 t = 32/8
 t = 4 hours