Question 902767
let x be speed (mph) for round trip
for the outbound
d= 200mile
r= 60mph
t= 200/60h

for the return trip
d= 200mile
r= 39mph
t= 200/39h

total distance is 400 mile
total time is (200/60)+(200/39) h

400=x((200/60)+(200/39))
solve the equation, you will find the unknown. 
which is approximately 47.273h