A reactor vessel is filled with a first-order reaction mixture at time t = 0. The reaction rate, in moles per liter per minute, is given by:

-r = kC

where C is the concentration of the reactant, in moles per liter, and k is the reaction rate constant, in liters per mole per minute. At time t = 0, the concentration of the reactant is C_0. The concentration of the reactant after time t is given by:

C(t) = C_0 e^(-kt)

Determine the time, in minutes, required for the reactant concentration to decrease to one-tenth of its initial value.