This guide will help you how to get the Backwards Pro/Backwards Expert achievement.

Step 1: Launch Drift.wav (the game)
Step 2: Choose any car and gamemode you want
Step 3: Press "S and D" or "S and A" to go backwards (you need like 20 metres of distance to do this)
Step 4: Once you completed Step 3, press S and you will earn money.
Step 5: To not lose control press A while pressing S to go right, and if you want to go left, press D while pressing S.
Step 6: Done. You need to earn $50 (in-game) for Backwards Pro and for Backwards Expert, you need to earn $100 (again, in-game)

Done.