Flare is shot up with an upwards velocity of 30m/s

The height of the flare is given by:

d) Determine the instantaneous velocity of the flare at t = 3 seconds by using the slopes of secants (1 mark for table, 2 marks for slopes)

I'm not really sure what I'm suppose to do, I know how to get slopes of secants but I dont have any secants..... Can someone just help explain the question....thanks