To rearrange the formula \( y = mx + b \) in terms of \( x \), the first step you should take is to subtract \( b \) from both sides of the equation.
This will give you:
\[ y - b = mx \]
This step isolates the term involving \( x \) and is the most logical first step for solving for \( x \). After that, you can divide by \( m \) to solve for \( x \).