Java

class stringedit{
    public static void main(string[]args){
        String testString = "20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39";
        String finalString=""; // MAX 5 NUMBERS EACH LINE
        int testlength = testString.length();
        for (int i=0;i<testlength;i++){
            finalString = finalString+testString.substring(i,i+14)+"\n"
			i+=14;
        }// END FOR
    }// END MAIN
}//END STRINGEDIT