4-5 r A = 25 - (1 0.005 200)2 25 + · = 18.75 kg/m3 Verify the solution At t = 0, from (E-5); r A = 0, as t fi ¥, r A = 25 kg/m3 The following example requires numerical integration. Example 4.1-4. 3A gas storage tank with a floating roof receives a steady input of 540 m /h of a natural gas. The rate of withdrawal of gas from the tank, Fw (m3/min), varies more or less randomly