A small mailbag is released from a helicopter that is descending steadily at 2.00 m/s. After 5.00s what is the speed of the mailbag

The acceleration of gravity (on Earth) is 9.8 m/s² downward.

This means that every falling object gains 9.8 m/s more downward speed

every second that it falls.

In 5 seconds of falling, it gains (5 x 9.8 m/s) = 49 m/s of downward speed.

If it was already descending at 2.0 m/s at the beginning of the 5 sec,

then at the end of the 5 sec it would be descending at

(2 m/s + 49 m/s) = 51 m/s.