To rearrange the formula \( a = p + PRT \) to isolate \( r \), we first need to identify how to manipulate the equation.
- Subtract \( p \) from both sides (Choice A): This would result in \( a - p = PRT \). This step gets us closer to isolating \( r \) because it removes \( p \) from the right side of the equation, which contains terms involving \( r \).
At this point, the equation looks like this: \[ a - p = PRT \]
Next, we would want to isolate \( r \).
- Divide both sides by \( PT \): This is the next logical step to isolate \( r\). If we assume \( P \) and \( T \) are non-zero, you can rewrite it as: \[ r = \frac{a - p}{PT} \]
So, the correct first step to rearranging the formula \( a = p + PRT \) with respect to \( r \) is A: Subtract \( p \) from both sides of the equation.