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Let the length = l
breadth = b 
height = h

given that l+b+h = 19
and diagonal = 11

We know that
(l+b+h)^2=l^2+b^2+h^2 + 2(lb+bh+lh)\\ \\ \Rightarrow19^2=121+2(lb+bh+lh)\\ \\ \Rightarrow 2(lb+bh+lh)=361-121\\ \\ \Rightarrow2(lb+bh+lh) = 240

But 2(lb+bh+lh) is the total surface area or simply "surface area" of the cuboid.
So surface area is 240cm².

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