A simply-supported beam has a circular cross-section with diameter \(20 \, mm\),
area \(A = 314.2 \, mm^2\), area moment of inertia \(I = 7854 \, mm^4\), and length \(L = 4 \, m\).
A point load \(P = 100 \, N\) acts at the center and an axial load \(Q = 20 \, kN\) acts through the centroidal axis.

The magnitude of the offset between the neutral axis and the centroidal axis, at \(L/2\) from the left, is ............ mm (rounded off to one decimal place).