A line can be extended infinitely in both the directions. Whereas a line segment is a part of a line that is bounded by two distinct end points.

Alternate exterior angles are equal.

Therefore, the required angle = ${80}^{\circ }$

When a transversal cuts two lines such that pairs of alternate interior angles are equal, then the lines have to be parallel. The interior alternate angles are always equal for a pair of parallel lines.

Obtuse angles are greater than ${90}^{\circ }$ . So, the sum of two such angles will be greater than ${180}^{\circ }$​.

Therefore, two obtuse angles cannot be supplementary.

Three lines can intersect at one point as shown below:

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A clock has a total of 360°.
The angle between any two consecutive numbers on a clock  
= $\frac{{360}^{\circ }}{12}$ = 30${}^{\circ }$​ [$\because$ a clock has 12 divisions]

At 8 o'clock, the minute hand is at 12 and the hour hand is at 8 and there are 4 divisions between 8 and 12. 

$\therefore$ The angle between them  = 4 × 30${}^{\circ }$
                                               = 120${}^{\circ }$
Hence the angle formed at 8 o'clock is an obtuse angle since it is more than 90° and less than 180°.

From the figure given in the question, we can observe that
$\angle$3 = 75${}^{\circ }$
(Vertically opposite angles)
$\angle$2 +75${}^{\circ }$ = 180${}^{\circ }$
(Angles on a straight line)
$\Rightarrow$ $\angle$2 = 180${}^{\circ }$- 75${}^{\circ }$ = 105${}^{\circ }$
$\angle$2 = $\angle$4
(Vertically opposite angles)
$\Rightarrow$$\angle 4$ = 105°

Exterior angles lie outside the parallel lines. The exterior angles are 1, 2, 7, 8.

Two angles are called supplementary angles if their sum is 180${}^{\circ }$.

So, 30${}^{\circ }$ + 2x = 180${}^{\circ }$

Hence, x = 75${}^{\circ }$.

A circular clock consists of 360 degrees.  The angle between any two consecutive numbers of a clock is.

$\frac{360}{12}$ = 30${}^{\circ }$​.

At 2 PM, the minute hand is at 12 and the hour hand is at 2.

Therefore the angle between them  = 2 × 30 = 60${}^{\circ }$​