To solve for \( x \) in the problem where two adjacent angles measure \( x^\circ \) and \( (x + 30)^\circ \) that form a 90° angle, you can set up the following equation:
\[ x + (x + 30) = 90 \]
Combine like terms:
\[ 2x + 30 = 90 \]
Subtract 30 from both sides:
\[ 2x = 60 \]
Divide by 2:
\[ x = 30 \]
So the value of \( x \) is \( 30 \).
Thus, the correct response is:
30