Micah has an electricity plan where he is charged a monthly fixed rate of $3.73 and a usage fee of $0.10 per kilowatt-hour. In the equation below, x represents the amount of electricity he used, and y represents the amount Micah was charged for electricity.
y = $0.10x + $3.73

If Micah was charged $103.73 for electricity last month, how much electricity did he use?