An angle whose measure is $90^{\circ}$ is called a $\ldots \ldots \ldots$

The measures of two vertically opposite angles are $(5x + 30^{\circ})$ and $(8x - 60^{\circ})$,then the value of $x = \dots$

Prove that two lines that are respectively perpendicular to two intersecting lines intersect each other.

The angles of a triangle are in the ratio $2: 3: 4$. Find the angles of the triangle.

If the measure of an acute angle is $x^{\circ}$,find the difference of the measure of its supplementary angle and complementary angle. (in $^{\circ}$)

If one of the two angles of a linear pair has measure $75^{\circ}$,the measure of the other is $\ldots \ldots \ldots$ (in $^{\circ}$)