Explanation:
Just find the value-added of each titration
Final volume - Initial volume = volume added
so for the 1st titre value it will be
16.60-11.80 = 4.8cm^3
for second it will be
16.65-9.75 = 6.9cm^3
to average it add them and divide by the total number of trials
which is 4.8+6.9 =11.7
and then divide by 2
which is 11.7/2 = 5.85 cm^3 of average volume added