pich1package/bin/main.js

I hope work

var path = require('path');
var fs = require('fs');
var lib = path.join(path.dirname(fs.realpathSync(__filename)), '../lib');

var simple = require(lib + '/simple_math.js');
var advance = require(lib + '/advance_math.js');

module.exports = {
    add: simple.addition,
    sub: simple.subtraction,
    mul: advance.multiply,
    divi: advance.division
}