The graph shows a function that models the value V in millions of dollars of a stock portfolio as a function of time T in months over an 18-month period on what interval is the function decreasing on what interval is the function increasing

Since there is figure provided, I can't give an exact answer. But assuming the relationship is linear, there could only be two cases possible. For Case 1, the slope is decreasing. This means that interval T increases, while interval V decreases. The other case is when the slope is increasing. This means that both intervals T and V are increasing.