The denaturalization process implies the process in which the proteins lose their structure (quaternary, tertiary, and secondary) when exposed to chemical denaturants or heat, between other factors.
If the enzyme's effective temperature range is between 60ºC and 80ºC, then it will not be denaturalized when exposed to temperatures within this range. So, neither a temperature of 65ºC nor a temperature of 80ºC will denaturalize the protein.
The optimum pH of the enzyme is 3, the same as before, if the protein works well at this pH, then it will not lose its shape in this acid environment. Even if small changes in the acidity tend to make the proteins denaturalize, a pH of 3.1 is too weak to affect enzyme A, at most, you will observe a decrease in its functions.
But a pH of 9 is far enough from the optimum pH of enzyme A to consider the possibility of denaturalization.
The enzyme A is expected to denaturalize at a pH=9