$A$ straight angle has measure......... (in $^{\circ}$)

In $\Delta ABC$,$\angle A + \angle B = 80^{\circ}$ and $\angle B + \angle C = 150^{\circ}$. Find the measure of each angle of $\Delta ABC$.

If one of the angles formed by two intersecting lines is a right angle,what can you say about the other three angles? Give reason for your answer.

In the figure,$x=y$ and $a=b$. Prove that $l \parallel n$.

In the figure,$AB$,$CD$,and $EF$ are three lines concurrent at $O$. Find the value of $y$. (in $^{\circ}$)

In the following figure,lines $AB$ and $CD$ intersect at $O.$ If $\angle AOC + \angle BOE = 100^{\circ}$ and $\angle BOD = 40^{\circ},$ find $\angle BOE$ and reflex $\angle COE.$