To solve for \( x \) in the two adjacent angles measuring \( x° \) and \( (x + 30)° \) that together make a \( 90° \) angle, you can set up the following equation:
\[ x + (x + 30) = 90 \]
Now, simplify the equation:
\[ x + x + 30 = 90 \]
\[ 2x + 30 = 90 \]
Next, subtract \( 30 \) from both sides:
\[ 2x = 90 - 30 \]
\[ 2x = 60 \]
Now, divide by \( 2 \):
\[ x = \frac{60}{2} = 30 \]
So, the measure of the angle \( x \) is \( \boxed{30} \).