How do I calculate speed in a velocity-time graph? Displacement-time graph?

[kimi8]

Homework Statement

How do I calculate speed in a velocity-time graph? And in a displacement-time graph?

Homework Equations

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The Attempt at a Solution

I'm quite at a lost at how to calculate these =S
Any help is appreciated.

 

[LowlyPion]

If your graph is V_(t) vs. t then isn't the graph at any point the V at that particular t?

For displacement and time, what is the definition of speed? Change in displacement for a change in time? And if you examine an extremely small time change at a point then what is that?