To show that angles on a straight line always add up to 180 degrees, let’s make it simple:

1. What is a Straight Angle? A straight line makes a straight angle. This angle measures exactly 180 degrees.

2. Next to Each Other Angles: When two angles sit right next to each other on a straight line, they share a side.

3. Adding Angles Together: If you put the sizes of these two angles together, they fill up the entire straight angle.

So, if you have angle A and angle B on a straight line, it means:

$A + B = 180^\circ$

Just remember, it’s all about seeing how these angles complete the whole angle of the line!