It will take 3 * 5 = <<3*5=15>>15 minutes to brush his cats.
All together, it will take 45 + 60 + 30 + 15 = <<45+60+30+15=150>>150 minutes to clean his apartment.
In three hours, there are 60 * 3 = <<60*3=180>>180 minutes.
Thus, he will have 180 - 150 = <<180-150=30>>30 minutes of free time remaining.
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