The nJoy Devi B700 is a budget tablet, running Android 4.2.2 on a dual-core Actions ATM7021 at 1.2Ghz and 1 Gb of RAM; other specs are 8 Gb of storage and a 7 in. screen.
It seems to be using the same firmware – gs702c – as a P706 tablet, one that is a bit more heard of on the internet, so the same method of rooting works.
Start by activating USB debugging on the tablet (Settings > Developer Tools > Enable USB Debugging), then connect it to your computer.
Windows will attempt to install several devices. If all is good, move on. If one device fails to find a driver, use this driver to install the ADB interface.
After everything is working properly, run RootGenius and click QuickRoot.
If RootGenius fails to find your device, make sure it is correctly detected. You can run adb devices in a command prompt to check the device is available. If it is not, try to uninstall it and/or re-install it using the driver linked above.