The table will contain times (sec) in one column.  The second column is your rates per interval.
The first one is easy.  The interval is 10 seconds-X value.  You will divide the amount of H₂O₂ decomposed in 10 sec by 10 sec.  That will be the value for Y.  

The second one is for 30 seconds-X.  Now calculate Y.  Take the total amount decomposed in 30 seconds and subtract from that the amount already decomposed in 10 second interval.  Divide by the number of seconds in the second interval-20 sec (30-10).  That is your next Y value.  

What does this graph indicate?  In the first 10 seconds, there was a lot of substrate and a lot of enzymes.  Much of the substrate was decomposed.  Then briefly, all the enzymes were busy and nothing much happened.  During the next 60 seconds, there were plenty of enzymes free, but there was little substrate left to decompose; consequently the rate increased over the 60 second time interval, but then the rate flattened out.  There were enzymes to work, but no substrate on which to work.