Water is pumped into a storage tank at a variable rate given, in litres per minute, by R(t)=at2+6, where t is the time in minutes (t≥0) and a is a constant. The volume of water in the tank at time t minutes is V(t)=∫R(t)dt. It is known that the tank is empty at t=0 and that it contains 160 litres after 4 minutes.
(i) Obtain the expression for V(t), including the constant of integration C.
(ii) Using the condition V(0)=0, determine the value of C.
(iii) Using the additional information V(4)=160, calculate the value of a.