Calculate the average sound reduction across the following external wall:
Wall: 225mm solid brick, plastered one side, 3.70m long and 2.65m high. SRI = 48dB
Window: Double glazed 1.80m x 1.20m high. SRI = 28dB
External door: 44mm thick, solid core flush door. 900mm x 2.00m high. SRI = 25dB
