How can the velocity of an object at any given instant in time be determined from a velocity-time graph of its motion?

Can anybody me with this? ? (picture included.)

6–43 a food department is kept at 2128c by a refrigerator in an environment at 308c. the total heat gain to the food department is estimated to be 3300 kj/h and the heat rejection in the condenser is 4800 kj/h. determine the power input to the compressor, in kw and the cop of the refrigerator.

What was the first instrument to ever record an earthquake?