Answer:
-7.66 x 10^-5 mol/L per second.
Step-by-step explanation:
You find the avg. rate of decomposition by finding the overall amount of matter decomposed and dividing it by the time the mixture/substance decomposed for. In this case, it would be (0.1054 mol/L - 0.1103 mol/L ) / 64.0 s.
This gives you -0.0000766 mol/L per second (using significant figures rules), or -7.66 x 10^-5 mol/L per second.
Cheers.