For a quantity whose rate of change is given by a continuous function r(t) (units per hour) and whose initial amount is zero, the accumulated amount after t hours is A(t)=∫0tr(s)ds. To find the time T at which the accumulated amount first equals a fixed value K units, which of the following equations should be solved for T?
a) r(T)T=K
b) ∫T0r(s)ds=K
c) ∫0Tr(s)ds=K
d) ∫0T∣r(s)∣ds=K