Let \( m \) be the monthly membership fee.
In May, Rosa took 4 cycling classes, so her total cost can be expressed as:
\[ \text{Total Cost} = m + 5 \times 4 \]
This simplifies to:
\[ \text{Total Cost} = m + 20 \]
We know from the problem that this total cost was $55, so we can set up the equation:
\[ m + 20 = 55 \]
Solving for \( m \):
\[ m = 55 - 20 = 35 \]
So the monthly membership fee is \( m = 35 \).
In June, her total cost was equal to twice the membership fee:
\[ \text{Total Cost in June} = 2m = 2 \times 35 = 70 \]
Let \( c \) represent the number of cycling classes Rosa took in June. Therefore, her cost in June can be expressed as:
\[ 70 = m + 5c \]
Substituting \( m = 35 \):
\[ 70 = 35 + 5c \]
To find \( c \), we rearrange the equation:
\[ 70 - 35 = 5c \] \[ 35 = 5c \] \[ c = \frac{35}{5} = 7 \]
So, Rosa took 7 cycling classes in June.
The answer is 7.