Can someone elp me how do I blow up the tank. I can manage to take out some of the surrounding enemies but the n zap I'm dead

The key is the ruined section of the building you come through. Send your men on through the first gap on the left to the cover on the enemy's right flank west of the carpark. Don't follow them through and don't worry about the enemy infantry. Arm your rocket launcher straight away and move further along inside the building until you reach another gap which gives you a clear shot at most of the carpark. Once the tank enters just blow it away and mop up the men.

If you're a silly billy and didn't pay attention to the default loadout, opting insteand to remove the launcher (or if you manage to miss the target with your rocket), you still have the option of picking up an enemy RPG near the booth at the north-west corner of the carpark. To do this, order you men to the same cover as the previous tactic and use that same cover to get to the booth. A gap in the fence allows you through so you can get a clear shot at the side of the tank. You may have to take out the enemy infantry first to make that shot. Just remember that the longer you take the more chance your men will be killed by the tank.