I have found a way to earn this trophy with ease. First I'll tell you what trophy requires you to do? Keep It Up Trophy - Complete a Round with a Kills-per-minute ratio of 100 or more. First get 2 levels of ammo for SMG and how much it can carry. Why? Because first area your going to hit is Armor area. So you will need to head right. At this time you will not level rifle at all you wont need it.
Round 1 (Armor Area Red): See how quickly you can gather zombies and kill them fast enough before timer runs down. Your gonna take door on the left which allows you to upgrade armor. (Note: you will not grab the armor when your doing this.)
Round 2 (Money Area Yellow): This is quite simple gather as much money as you can. Instead of going to left for health area you'll be going to right to find all money chests.
Now after you complete round 2 your going to level all stats of SMG until there 25,000 each for last level.
Round 3 (Armor Area Red): Now this were you will need to watch what you are doing kill all zombies expect cutter which would come down. Once again take door on left and keep mowing down those zombies. By time you reach area where you need to kill everything to complete round 3 you should be sitting at 103.5 maybe more depending how good you are. Once you go through doors and they close you will get trophy.
HAPPY HUNTING - AnimeInfection