To represent the relationship between the measures of the two adjacent angles inside a \(90^\circ\) angle, you can set up the equation as follows:
The first angle is \(x + 18\) degrees, and the second angle is \(x\) degrees.
Since they are adjacent angles inside a \(90^\circ\) angle, their measures should add up to \(90^\circ\). The equation representing this relationship is:
\[ (x + 18) + x = 90 \]
So, filling in the blanks in your format, it becomes:
\[ (x + 18°) + x = 90° \]