I see from the given data that each additional carpet after the first costs $50 each to have cleaned.
The first costs $125. Supposing we subtract $50 from that, we get $75. So, it sounds like it costs $75 just to get the carpet cleaners to your house.
The rule would then be $75 + $50x, where x : {1, 2, 3, 4, .... }
Let's check this result. Suppose x = 1. Will the charge be $125, as show in the table? $75 + $50(1) = $125. Correct.
Suppose x = 4. Will the charge be $275 as shown in the table?
$75 + $50(4) = $275. YES