So,
The first thing we're going to remember is the equation that we're going to use to find the average rate of disappearance of a reactive.
Given a reaction of the form:
We're given the reaction:
Now, we only need to replace in the equation:
The average rate of dissapareance of NO2 over the time period from t=10s to t=20s, is 0.00381 M/s.