6. A point \( (x, y) \) is moving along a curve \( y = f(x) \). At the instant when the slope of the curve is \( \frac{3}{4} \), the x-coordinate of the point is decreasing at the rate of \( \frac{2}{5} \) units per second. The rate of change, in units per second, of the y-coordinate of the point is
