For the first set of walls, each wall covers 3 meters wide * 2 meters tall = <<3*2=6>>6 square meters.
There are two of these walls, so this becomes a total of 6 meters * 2 walls = <<6*2=12>>12 square meters.
The third wall covers 5 meters wide * 2 meters tall = <<5*2=10>>10 square meters.
The final wall covers 4 meters wide * 2 meters tall = <<4*2=8>>8 square meters.
So in total, the paint needs to cover 12 + 10 + 8 = <<12+10+8=30>>30 metres.
Since each can covers 2 meters, Lucille needs 30 meters / 2 = <<30/2=15>>15 cans of paint.
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