The half life of a reaction of a compound A to give compounds D and E is 8.50 min when the initial concentration A is 0.150 mol/L. how long will it take for the concentration to drop to 0.300 mol/L.

Hang on Adrienne, something is wrong with my calculator: it keeps telling me that if the concentration starts at 0.150M and goes to 0.300M it is RISING, not DROPPING,