Part A:
Let \( h \) represent the number of hours the electrician worked.
Now the total cost can be expressed with the following equation based on the given charges:
Total bill = One-time fee + (Hourly rate × Number of hours) \[ \text{Total bill} = 60 + 55h \]
In this problem, the total bill is $252.50, so we can write the equation as: \[ 252.50 = 60 + 55h \]
Thus, the variable defined for this problem is \( h \), the number of hours worked by the electrician.