5 hours in the studio is the same as 5 * 60 = <<5*60=300>>300 minutes.
To record all of his songs, Elvis takes 12 * 10 = <<12*10=120>>120 minutes.
After editing and recording 300 – 120 – 30 = <<300-120-30=150>>150 minutes are left to write all of his songs.
Songwriting therefore took 150 / 10 = <<150/10=15>>15 minutes per song.
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