'inverter' and 'or' gate starts at the same time while 'and' gate waits for 'inverter' output.
# - 'inverter' and 'and' gate are serially connected so time required is 6+10=16ns.
$ -'or' gate requires 11ns.
# and $ is parallely connected so total time required is max(#,$) =max(16,11) =16ns.
Total time required is 16ns.
(i am not sure...its my answer)