Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
The two events associated with this measurement are:
$\bullet$ The first event is the start of the flight: This event marks the beginning of the flight when the airplane takes off from Los Angeles.
$\bullet$ The second event is the end of the flight: This event marks the completion of the flight when the airplane lands in New York.
$$\color{blue}{\bf [b]}$$
The person on the airplane, $\bf your\; friend$, measures the proper time. The proper time is the time experienced by an observer in their own reference frame. In this case, your friend on the airplane is measuring the time using the stopwatch she carries, which corresponds to her proper time.
$$\color{blue}{\bf [c]}$$
According to Lorentz Transformation,
$$t'=\dfrac{t-\frac{vx}{c^2}}{\sqrt{1-\frac{v^2}{c^2}}}$$
$\bf your\; friend$, measures the shorter time of the flight.
