please explain this part to me properly I am not getting why you are writing 2.2 X + Y I am not getting that please explain it to me

perimeter of original rectangle = l + b + l + b = 2(l + b)
perimeter of new rectangle = 2l + 2b + 2l + 2b = 4(l + b)
ratio = 2(l + b) : 4(l + b)
        = 1(l + b) : 2(l + b)
        = 1 : 2
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