ah, now thats a question i wanted to answer.. lol
To get a B ranking, just beat the game in under three hours, which you already got. then go into your safe box and there you will see your infinity sub- machine gun.
or
Play the first scenario with either character. Enter your finger print on the computer in the giant moth room. When you get to the door where you need your finger print to enter, enter your finger print and choose not to continue. Finish the game and save. Play off of the game you saved with the next character and follow the same process and put in the second finger print. The door will unlock and inside will be a few Lickers and a sub-machine gun.
and thats because you used your infinity Weapons, one shoot and it goes straight to B ranking, but since u said 2h20 min you took some time, either you pause it for long, or you forgotten something so you had to go back and get it or other things in this game that can be fustraiting. etc. hard to kill zombies, lickers and so on...
when i played and used the Infinity Rocket Launcher and finished the first senario with leon, my time was like 1 hour and something mins and a B Ranking cause i used the Rocket Launcher, but without all those infinity weapons and complete the game, maybe an S or an A and depends your hour.
