Answer:
a) 0.000112 M/s is the average reaction rate between 0.0 seconds and 1500.0 seconds.
b) 0.00011 M/s is the average reaction rate between 200.0 seconds and 1200.0 seconds.
c) Instantaneous rate of the reaction at t=800 s :
Instantaneous rate : 
Explanation:
Average rate of the reaction is given as;

a.) The average reaction rate between 0.0 s and 1500.0 s:
At 0.0 seconds the concentration was = 

At 1500.0 seconds the concentration was = 

![R_{avg]=-\frac{0.016 M-0.184 M}{1500.0 s-0.0 s}=0.000112 M/s](https://tex.z-dn.net/?f=R_%7Bavg%5D%3D-%5Cfrac%7B0.016%20M-0.184%20M%7D%7B1500.0%20s-0.0%20s%7D%3D0.000112%20M%2Fs)
0.000112 M/s is the average reaction rate between 0.0 seconds and 1500.0 seconds.
b.) The average reaction rate between 200.0 s and 1200.0 s:
At 0.0 seconds the concentration was = 

At 1500.0 seconds the concentration was = 

![R_{avg]=-\frac{0.019 M-0.129M}{1200.0s-200.0s}=0.00011 M/s](https://tex.z-dn.net/?f=R_%7Bavg%5D%3D-%5Cfrac%7B0.019%20M-0.129M%7D%7B1200.0s-200.0s%7D%3D0.00011%20M%2Fs)
0.00011 M/s is the average reaction rate between 200.0 seconds and 1200.0 seconds.
c.) Instantaneous rate of the reaction at t=800 s :
At 800 seconds the concentration was = 

Instantaneous rate : 