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The surface area A of a steel cylinder is given by the formula

A= 2.pi.r²+2.pi. r h
Where r is the radius and h the height
a) find the required radius if A = 12500mm² , and h = 150mm
b) Determine the number of 2.5 liter tins of paint that are needed to coat 500 cylinders with a thickness of 20µm
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