1. Download APK first, then copy to your Android device's SD card

2. Install APK, DO NOT open app

3. Download obb files, then rename to 'main.15.com.spilgames.operatenow.animal.hospital.obb'

4. Copy obb file to /SDCARD/Android/obb/com.spilgames.operatenow.animal.hospital/main.15.com.spilgames.operatenow.animal.hospital.obb