The bar has a cross-sectional area of $400\left(10^{-6}\right) \mathrm{m}^{2}$. If it is subjected to a uniform axial distributed loading along its length and to two concentrated loads, determine the average normal stress in the bar as a function of $x$ for $0.5 \mathrm{m}<x \leq 1.25 \mathrm{m}$