Answer
The new length of the aircraft = 41.086 m
Work Step by Step
Previous length of the aircraft = 41.05m
The new length of the aircraft = 41.05 m + 3.6 cm (length of the antenna)
When we are adding two physical quantities both of them should have the same units. Therefore we can convert centimeters into meters and solve the problem as follows.
$3.6 cm = 3.6\times10^{-2} m$
$\space\space\space\space\space\space\space\space\space\space = 0.036 cm$
So we can calculate the new length by using the above value,
New length of the aircraft $=41.05 m+ 0.036 m=41.086 m$