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.

Two unknowns:

let the number of miles driven be m
let the number of hours he drove be t.

expense for that driver = 2m + 25t = 625
speed = distance / time
50 = m/t
m = 50t

the system of equations (that's all you asked for)
2m + 25t = 625
m = 50t

I assume you would use substitution to solve them,
comes out very nice and straighforward