The thermal insulation used in building is commonly rated in terms of its R-value, defined as d/k, where d is the thickness of the insulation in inches and k is its thermal conductivity. In the United States, R-values are expressed in British units. For example, 3.0 in. of foam plastic would have an R-value of 3.0/0.30 = 10, where k = 0.30 Btu ∙ in./(ft2 ∙h∙ oF). This value is expressed as R-10.
(a) Better insulation has a (1) high, (2) low, or (3) zero R-value. Explain.
(b) What thicknesses of (1) Styrofoam and (2) brick would give an R-value of R-10?

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