Since the one time fee is $30 and for each hour you get charged $25, we can write the following equation to represent this situation:
where 'x' is the number of hours and 'y' is the total cost.
In this case, Nicolepaid $155, then, we can make y = 155 and solve for x to find how many hours did it take to clean the car:
we have that x = 5, therefore, it took 5 hours to clean Nicole's car