d A line with a gradient of $-\frac{2}{5}$ and passing through $D(15,-9)$.

Step 1 ：Given the gradient $m = -\frac{2}{5}$ and the point $D(15, -9)$

Step 2 ：Use the point-slope form of a linear equation: $y - y_1 = m(x - x_1)$

Step 3 ：Plug in the values: $y - (-9) = -\frac{2}{5}(x - 15)$

Step 4 ：Simplify the equation: $y = -\frac{2}{5}x - 3$

Step 5 ：\(\boxed{y = -\frac{2}{5}x - 3}\)