$3-$ A level was set up exactly mid$-$way between two pegs A and B lying $100m$ apart and the following reading were obtained:

Reading at $A=1\mathrm{.}3m$ at $B=1\mathrm{.}7m$

The instrument was then set over A and the following readings were obtained

Height of level at $A=1\mathrm{.}75m$

Reading at $B=2\mathrm{.}1m$

a$)$ Calculate the collimation error of the level and express it as an angle of elevation and depression.

b$)$ The level was used in a levelling process, It was used to measure points $x$ and $Y.$ and the following readings were observed: Reading at $x=2\mathrm{.}98m$ Reading at $Y=3\mathrm{.}44m.$ Find the corrected readings on both stations if the instrument had a collimation error of