Search the internet for basic tutorials on using the Android NDK.
If you can create a java class that interfaces the native C functions - allowing the C functions to be called from java - then you can compile both the C and java class into a B4A library.
You can then call the java class methods from B4A and the java class will call the native C functions.
It might be helpful if you looked at the source code of an existing B4A library that does this - i have various libraries i could let you have the source code for if you are interested.
Martin.