Air at 90° C flows in a copper tube (k = 384 W/mK) of 4 cm inner diameter and with- 0..6 cm thick walls which are heated from the outside by water at . 125°C. A scale of 0.3 cm thick_ is deposited on the outer surface of the tube .whose · thermal conductivity is 1.75 W/mK. The air and water side unit surface conductance are 221 and 3605 W/m2K respectively. Find (a) the overall water to air transmittance, (b) water to air heat exchange and (c) temperature drop across the scale deposit.