Crisis For Alex

So in between building jobs etc today I heard loud crying coming from the office. I enquired and Alex said the printer wasn't handling colour properly. I said "Ink?" he said "No, someone has just changed the cartridge" but they hadn't used the expensive versions that we had to go to Tesco to buy. It wasn't seeing the ink or summat. So he did loads of PC repairing then got a new expensive Tesco's cartridge, fitted that instead and instantly that worked. So as Timmy has the same printer (and possibly brought the cheap replacement) he has a couple of cartridges to take with him and see if they work on his printer. How much should I charge him?

But it's all fixed now, so phew