Complementary angles are two angles that add up to \(90^\circ\). Given the angles \(3x^\circ\) and \((4x + 1)^\circ\), we can set up the equation:
\[ 3x + (4x + 1) = 90 \]
Simplifying this gives:
\[ 3x + 4x + 1 = 90 \] \[ 7x + 1 = 90 \]
Now, rearranging this gives:
\[ 7x + 1 = 90^\circ \]
Thus, the correct response among the options listed is:
\[ (7x + 1)^\circ = 90^\circ \]
The closest match in the provided responses is:
\[ (7x+1)°=90° \]