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From the condition, you know that the ratio of surface areas is 0.64 smaller to larger.
It means that the ratio of linear dimensions of the cylinders is
= 0.8 smaller to larger.
Now, you are given that the height of the larger cylinder is 200 cm.
Hence, the height of the smaller is 0.8 of it, i.e. 0.8*200 = 160 cm. ANSWER
Solved.