Travel 75 kilometers by land vehicle.

The description explains this one easily & you will most likely get this from just playing the game through normally. Any land vehicle counts towards the number of kms driven (cars, tanks, jeeps, motorcycles etc). When you reach a certain number of kms you will see a small notice at the top of the screen. Alternatively you can open your PDA, press & go into statistics, you can see how far you have driven in here.