Pseudoephedrine hydrochloride is an allergy medication. The polynomial L(t) = 0.03t4 + 0.4t3 – 7.3t2 + 23.1t, where 0 <= t <= 5, models the level of pseudoephedrine hydrochloride, in milligrams, in the bloodstream of a patient t hours after 30 milligrams of the medicine have been taken.
At what times, to the nearest minute, does the level of pseudoephedrine hydrochloride in the bloodstream reach 12 milligrams?