Calculating acceleration from 2 tangent lines

[azn4lyf89]

I have a position vs. time graph which is slightly curved. I found the slope of 2 tangent lines which I know are the velocity. My question is how do I get the acceleration using these 2 slopes. One slope is 295cm/s and the other is 575cm/s. I know that avg acceleration is final velocity - initial velocity/ final time - initial time but because these points aren't at the initial and final times, I don't think I can use that.

 

[Clairefucious]

Then don't use final time in the acceleration equation! If acceleration is a constant, you can calculate it over any time interval.