A Node That Feeds Two Places

A tiny model is written as a computational graph. Its inputs are the data value $x$ and the parameters $w$ and $b$:

Look carefully at where $u$ is used: it feeds the addition node and the final multiplication node. Two arrows leave it.

One forward pass is run with

$x = 4, \qquad w = 3, \qquad b = -2$

A backward pass then follows, starting from $\dfrac{\partial L}{\partial L} = 1$.

What value does the backward pass deliver for $\dfrac{\partial L}{\partial w}$? Give the exact value.