Let's denote the number of balloons that Alexa popped as \( b \).
According to the problem, Krista popped 6 balloons, which is 1 balloon less than the number Alexa popped. We can express this relationship with the following equation:
\[ 6 = b - 1 \]
Now, to solve for \( b \), we can add 1 to both sides of the equation:
\[ 6 + 1 = b \]
This simplifies to:
\[ b = 7 \]
So, Alexa popped 7 balloons.