The problem is not that this is an "easy question", its just that it doesn't make much sense! You have a "negative gradient such as -3" but then what does "change to 0" mean? What is changing? Is what "counted as increasing as decreasing"? If a function has negative gradient in an interval, then the function value is decreasing in that interval. If the derivative of the function goes from -3 up to 0, then the derivative is increasing but, since that derivative is always negative in that interval, the function value itself is decreasing.