Jonny's first step in solving the equation \( 8 + 3n = 20 \) is to subtract 8 from both sides because 8 is attached to 3n by addition. By subtracting 8 from both sides, he isolates the term containing \( n \) and simplifies the equation, making it easier to solve for \( n \). Thus, the correct response is:
8 is attached to 3n by subtraction.