It's probably hard to tell because of the computer voice, but the two words are pronounced differently. "er" sounds very similar to the English word "air" and "ihr" sounds very similar to the English word "here", just without the "h" (imagine a standard British accent).

You might want to listen to some professional audio recordings.

http://www.duden.de/rechtschreibung/er http://www.duden.de/rechtschreibung/ihr_sie_wem

(click on the speaker symbol)

Yes, I've been having the same problem. I'm very new to the German so I find it very difficult. When I ask the computer to pronounce it slowly, it sounds like "ee-er" (if you imagine the English pronunctiation of the vowels).

I had the same problem while doing the exercises here, but in real life speaking can tell the difference. It's true, it must be the computer voice. Thank you for the explanation.