Answer:
y=400*x-500
Step-by-step explanation:
The expression that represents the problem is:
y=400*x-500
Function y represents earnings for one day.
400 is the fixed number that is charge for one hour work
x represents the number of hours that the technician has worked for one day
To find the total earnings you should multiply the fixed charge for one hour work (400) by the number of hours worked in a day.
Then you need to substract the cost of gasoline in a day, it is 500 and it is a constant in the equation since it doesn't depend on the number of hours worked.
So, the function is:
y=400*x-500
