Air at \(1 \mathrm{~atm}\) and \(20^{\circ} \mathrm{C}\) is to be transported in a \(60-\mathrm{m}\)-long circular steel duct at a rate of \(5100 \mathrm{~L} / \mathrm{min}\). The roughness of the duct is \(0.25 \mathrm{~mm}\). If the pressure drop in the pipe is not to exceed \(90 \mathrm{~Pa}\), the maximum velocity of the air is

(a) \(3.99 \mathrm{~m} / \mathrm{s}\)

(b) \(4.32 \mathrm{~m} / \mathrm{s}\)

(c) \(6.68 \mathrm{~m} / \mathrm{s}\)

(d) \(7.32 \mathrm{~m} / \mathrm{s}\)

(e) \(8.90 \mathrm{~m} / \mathrm{s}\)