Let \( x \) be the number of hours Katherine worked last month.
The equation based on the problem statement is: \[ 60 = 5x + 3 \]
To find \( x \), we can solve the equation: \[ 60 - 3 = 5x \] \[ 57 = 5x \] \[ x = \frac{57}{5} \] \[ x = 11.4 \]
Therefore, Katherine worked 11.4 hours last month.