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

In $\Delta ABC$,$\angle B = \frac{\angle A + \angle C}{2}$ and $\angle A : \angle C = 1 : 2$. Find the measure of each angle of $\Delta ABC$.

In $\Delta XYZ$,$\angle X : \angle Y : \angle Z = 1 : 4 : 4$,then $\angle Z = \ldots$ (in $^{\circ}$)

In $\Delta ABC$,$\angle A = 2x - 10^{\circ}$,$\angle B = x + 10^{\circ}$,and $\angle C = 2x - 20^{\circ}$. Find the measure of each angle of $\Delta ABC$.

In the figure,if $AB \parallel CD \parallel EF$,$PQ \parallel RS$,$\angle RQD = 25^{\circ}$ and $\angle CQP = 60^{\circ}$,then $\angle QRS$ is equal to: (in $^{\circ}$)

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.