A research group developed the following mathematical model relating systolic blood pressure and age: P(x) = a + bln(x + 1), where P(x) is pressure, measured in millimeters of mercury, and a is age in years. By examining Guilford County hospital records, they estimate the values for Guilford County to be a = 37 and b = 27. Using this model, estimate the rate of change of pressure with respect to time after 28 years. Round to the nearest hundredth (2 decimal places). millimeters per year