To find the rate, you must divide the distance traveled by the time it took.
17.5 m is the distance while time it took was 5 seconds.
So,
17.5 ÷ 5 = 3.5 m/s
The rate of the anchor is 3.5 m/s
Note: I did not ignore the negative sign in the distance but rather acknowledged it as a magnitude. This meant that the anchor was dropping down instead of going up.