survaying class

A level network as shown in the following figure, where A$,$ B$,$ C$,$ and D are known errorfree points and their heights are $H_A=190\mathrm{.}200m,H_B=185\mathrm{.}498m,H_C=192\mathrm{.}764m$ and $H_D=178\mathrm{.}339m$ respectively. The observations are listed in the following table. It is assumed that all observations are uncorrelated. Please draw a level network diagram on the answer sheet, mark the average value of the backsight and forward sight differences on the diagram, and use an arrow to indicate the direction of the average height difference. Please use the Least Squares method to estimate $($a$)$ the a posterior unit weighted standard deviation; $($b$)$ the standard deviation of height difference observation per kilometer ; $($c$)$ Correction of each observation; $($d$)$ Heights of the points E and F ; $($e$)$ the standard deviations of the heights of two points E and F $.$

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