(a) When a bullet is fired into a sandbank, its retardation is equal to the square root of its velocity on entering. For how long will it travel if its velocity on entering the bank is 81 m s. 10. (b) A tank contains 400 litres of brine holding 100 kg of salt in solution. Water containing - kg of salt per litre flows into the tank at the rate of 12 litres per minute and the mixture, kept uniform by stirring, flows out at the same rate. As a result, one and a half kg of salt enters the tank each minute and 0.03q kg are removed, dq represented by the function = 1.5 0.03q where q denotes the number of kg of dt %3D salt in the tank at the end of t minutes. Find the amount of salt in the tank at the end of 90 minutes.