Basically, you have to understand the logic of a function.
If I plug in a value into V that represents the value of a milling machine, if I simplify the equation, I will be able to find x, the corresponding time to the value of the milling machine.
Knowing this logic, we can plug in $450,000 and $480,000, and then we will have two x-values. Then we can just find the range of the x-values to find our answer! :)
Let's go.
V = 750,000 - 120x
Plugged in 450,000 for V so now we can simplify the equation and find out what is the corresponding x-value for this value at this certain time.
450,000 = 750,000 - 120x
-450,000 -450,000
0 = 750,000 - 120x
+120x on both sides to isolate x
120x = 300,000
x = 2500
So, our first x-value in the range is 6250 hours. Now, let's plug in the larger value to find out the other x-value in the range.
V = 750,000 - 120x
480,000 = 750,000 - 120x
-480,000 -480,000
0 = 270,000 - 120x
Add 120x on both sides to isolate x
120x = 270,000
x = 2250
So, we found 2250 and 2500. So, the range of hours it corresponds to is 2250-2500.