need help on a particular question of my assignment...

Using strobe photography a badminton shuttle's path is followed. the strobe light takes photos every 0.2 seconds and lasts for a total of 3.2 seconds.

The actual positions of the shuttle are below...

Horizontal - 0.00 0.80 1.56 2.29 2.97 3.61 4.21 4.76 5.28 5.75 6.18 6.59 6.97 7.33 7.67 8.00 8.32

Vertical - 0.00 2.24 4.08 5.56 6.71 7.54 8.09 8.36 8.38 8.16 7.68 6.97 6.05 4.93 3.64 2.19 0.59

i plotted a graph of the horizontal position against time.

i am then asked to find the horizontal velocity of the shuttle using the gradient of the previous graph. it is supposebly a linear function and i just need to differentiate it. i think it may be y=ax^2+bx+c...i need a table and a graph.

not completely sure tho. help would be great. thanks.