Answer: 64.8 mph
Step-by-step explanation:
Given
Arriving time is 6 hours
return time is 4 hours
The average speed of returning 81 mph
Distance traveled while returning

the average speed of the entire trip is

** DISCLAMIER** am not completely sure. Please do not use my answer unless you are very desperate.
since O,R correspond with A,N I think you half F on each side and add it to 11.2 so
10 divided by 2 = 5
7 is already half.
5 + 7 is 12
12 + 11.2 = 23.2
IF THIS IS WRONG TRY 17
reason for 17:
10 + 7 = 17
If you look at both lines they look the same length as A, N.
By the binomial theorem,

Each term containing a factor 6 is divisible by 3, since 3 divides 6. The remaining 1 and 2 sum to 3, which is also divisible by 3.