The image shows two angles that form a straight line, where one angle is labeled $a$ and the other is $28^\circ$. Since these two angles are adjacent and form a straight line, they are supplementary, meaning their sum must equal $180^\circ$.

To find the missing angle $a$, we use the following equation:

$a + 28^\circ = 180^\circ$

Solving for $a$:

$a = 180^\circ - 28^\circ = 152^\circ$

Thus, the missing angle $a = 152^\circ$.

Would you like further details or have any questions about this problem?

Here are 5 related questions to deepen your understanding:

1. What are supplementary angles, and how do they relate to straight lines?
2. Can adjacent angles ever sum to something other than 180 degrees? Why or why not?
3. What is the relationship between complementary and supplementary angles?
4. How would the equation change if one of the angles were labeled with a variable rather than given a specific degree measure?
5. How can this knowledge of angle pairs help in solving problems involving polygons?

Tip: Always remember that adjacent angles on a straight line add up to 180 degrees, which is useful in many geometric problems!