Joshua owns a trucking company. For every truck that goes out, Joshua must pay the driver $25 per hour of driving and also has an expense of $2 per mile driven for gas and maintenance. On one particular day, the driver drove an average of 50 miles per hour and Joshua's total expenses for the driver, gas and truck maintenance were $625. Write a system of equations that could be used to determine the number of hours the driver worked and the number of miles the truck drove. Define the variables that you use to write the system.