From the information given, you can say that the total amount Tom's Landscaping charges for a job would be equal to the flat fee plus the result of multiplying the charge per hour for the number of hours and this would be:
c=y+25x (1), where:
c is the total cost
y is the flat fee
x is the number of hours
Now, as you know that Tom charged a customer $90 for a job that required 3 hours, you can replace c with 90 and x with 3 and solve for y to find the flat fee:
90=y+25(3)
90=y+75
90-75=y
y=15
Finally, as you know that the flat fee is 15, you can replace this value in (1) to establish the equation that would calculate the total amount that Tom's Landscaping charges for a job that requires x hours of work:
