If the two angles are complementary, their measures add up to 90 degrees. Given the angles are (2x + 3)° and 2x°, we can set up the equation as follows:
\[ (2x + 3) + 2x = 90 \]
This equation states that the sum of the angle measures (2x + 3)° and 2x° equals 90°.
To fill in the blanks in your question, we can write:
(2x + 3)° + 2x° = 90°